Carbon deposit friction lining material

ABSTRACT

The present invention relates to a friction material comprising a fibrous base material primary layer of less fibrillated aramid fibers, synthetic graphite and at least one filler material, and a secondary layer of a mixture of carbon particles and at least one retention aid coated on at least one surface of the primary layer. In certain embodiments, the fibrous base material is impregnated with a phenolic or phenolic-based resin material, including, for example, a mixture of a phenolic resin and a silicone resin to form a friction material having high heat resistance and high friction durability characteristics.

TECHNICAL FIELD

This is a continuation-in-part of Ser. No.08/704,899 filed Aug. 30,1996, still pending, which is a continuation of Ser. No.08/534,978 filedSep. 28, 1995, now abandoned, which is a continuation-in-part of Ser.No. 08/253,727 filed Jun. 3, 1994, now U.S. Pat. No. 5,753,356, which isa continuation-in-part of Ser. No. 08/101,951 filed Aug. 4, 1993,abandoned, all of which are expressly incorporated herein by reference.

The present invention relates to a friction material comprising afibrous base material having carbon particles adhered to the surface ofthe fibrous base material by a retention aid material. The fibrous basematerial comprises a primary layer having less fibrillated aramidfibers, manufactured or synthetic graphite and at least one fillermaterial, such as diatomaceous earth and a secondary layer having carbonparticles. The invention further relates to a composite frictionmaterial comprising the above described fibrous base materialimpregnated with a phenolic resin or a modified phenolic resin blend. Incertain embodiments, at least one silicone resin is blended with atleast one phenolic resin for use in impregnating the fibrous basematerial.

The friction material of the present invention has better "break-in"behavior and more stable coefficients of friction in the initial stagesthan conventional friction materials. Also, the resulting frictionmaterial is especially useful in high energy applications.

BACKGROUND ART

New and advanced transmission systems and braking systems are beingdeveloped by the automotive industry. These new systems often involvehigh energy requirements. Therefore, the friction materials technologymust be also developed to meet the increasing energy requirements ofthese advanced systems.

The friction material must be able to withstand high speeds whereinsurface speeds are up to about 65 m/seconds. Also, the friction materialmust be able to withstand high facing lining pressures up to about 1500psi. It is also important that the friction material be useful underlimited lubrication conditions.

The friction material must be durable and have high heat resistance inorder to be useful in the advanced transmission and braking systems. Notonly must the friction material remain stable at high temperatures, itmust also be able to rapidly dissipate the high heat that is beinggenerated during operating conditions.

The high speeds generated during engagement and disengagement of the newtransmission and braking systems mean that a friction material must beable to maintain a relatively constant friction throughout theengagement. It is important that the frictional engagement be relativelyconstant over a wide range of speeds and temperatures in order tominimize "shuddering" of materials during braking or the transmissionsystem during power shift from one gear to another. In particular, thefriction material must not shudder during the initial cycles or"break-in" period of operation.

Previously, asbestos fibers were included in the friction material fortemperature stability. For example, the Arledter et al. U.S. Pat. No.3,270,846 patent describes phenolic and phenolic-modified resins usedwith asbestos. Now, however, due to health and environmental problems,asbestos is no longer being used. More recent friction materials haveattempted to overcome the absence of the asbestos in the frictionmaterial by modifying impregnating paper or fiber materials withphenolic or phenolic-modified resins. These friction materials, however,do not rapidly dissipate the high heat generated, and do not have thenecessary heat resistance and satisfactory high coefficient of frictionperformance now needed for use in the high speed systems currently beingdeveloped.

While phenolic resins have found use in friction materials for wetclutch applications, the phenolic resins have various limitations. Thephenolic resin friction materials do not have the high heat resistancenecessary for use with the new high energy transmission systems. Inparticular, the phenolic resins carbonize at a temperature of about 450°to 500° C. which is too low to be useful in high energy applications. Inaddition, phenolic resins are rigid materials and when the phenolicresins are used in a friction material, uneven lining wear and separatorplate "hot spots" result.

Attempts to overcome the limitations and drawbacks of phenolic resinfriction materials include the replacement of phenolic resins with otherthermosetting resins. One attempt to produce friction materials involvesthe modification of a phenolic resin with various synthetic resins. Oneexample, described in Takarada et al. U.S. Pat. No. 4,657,951, is aphenolic resin modified with an organopolysiloxane which is compressionmolded to form a friction material. The phenolic resin andorganopolysiloxane are reacted together to effect a condensationreaction which is then distilled, solidified by cooling, and pulverizedto obtain a powdered phenolic-modified resin. The powderedphenolic-modified resin was used in forming a compression moldedfriction material.

As far as is known, there is no disclosure of a friction material foruse in transmission systems which includes a silicone material blendedwith a phenolic material and used to impregnate a friction paper.

While the Hartmann et al. U.S. Pat. No. 3,911,045 reference discusses asilicone material blended with phenolic resins for use as a compressionmolding composition, there is no disclosure or suggestion that asilicone material could successfully be blended with a resin materialand used to impregnate a friction lining material. On the contrary,previous attempts to use silicone resins in friction materials have beenunacceptable. A friction lining that is impregnated or saturated with asilicone resin has, in the past, demonstrated poor shear strength anddelamination resistance. Further, friction materials saturated with asilicone resin are usually too elastic and therefore tests withundesirable friction and wear characteristics resulting. It is notsurprising that molded friction lining compositions formed entirely of aphenol-formaldehyde resin-polysiloxane resin have not been used eventhough they are known, since such molded compositions do not have thenecessary constant coefficient of friction characteristics and suchfriction materials fail under high energy and high heat conditions.

The present invention is an improvement over the Seitz, U.S. Pat. No.5,083,650 reference which involves a multi-step impregnating and curingprocess; i.e., a paper is impregnated with a coating composition, carbonparticles are placed on the paper, the coating composition in the paperis partially cured, a second coating composition is applied to thepartially cured paper, and finally both coating compositions are cured.

In order for friction materials to be useful in "wet" applications, thefriction material must have a wide variety of acceptablecharacteristics.

The friction material must be resilient or elastic yet resistant tocompression set, abrasion and stress; have high heat resistance and beable to dissipate heat quickly; and, have long lasting, stable andconsistent frictional performance. If any of these characteristics arenot met, optimum performance of the friction material is not met.

Thus, it is also important that the impregnating resin be used with asuitable friction lining or fibrous base material to form a high energyapplication friction material. The friction material must have goodshear strength both when saturated with the wet resin duringimpregnation and when saturated with brake fluid or transmission oilduring use.

It is also important, under certain applications, that the frictionmaterial have high porosity such that there is a high fluid permeationcapacity during use. Thus, it is important that the friction materialnot only be porous, it must also be compressible. The fluids permeatedinto the friction material must be capable of being squeezed or releasedfrom the friction material quickly under the pressures applied duringoperation of the brake or transmission, yet the lining material must notcollapse. It is also important that the friction material have highthermal conductivity to also help rapidly dissipate the heat generatedduring operation of the brake or transmission.

Accordingly, it is an object of the present invention to provide animproved friction material with reliable and improved propertiescompared to those of the prior art.

A further object of this invention is to provide friction materials withgood anti-shudder performance, high speed and energy durability, highporosity and strength.

As a result of extensive research in view of the need for a betterfriction material, a friction material with improved characteristics hasbeen developed by the inventors. The present friction material isespecially useful in applications where the friction material issubjected to harsh "break-in" conditions during use.

DISCLOSURE OF THE INVENTION

In order to achieve the requirements discussed above, many materialswere evaluated for friction and heat resistant characteristics underconditions similar to those encountered during operation. Bothcommercially available brake linings and transmission materials wereinvestigated and proved not to be suitable for use in high energyapplications.

The present invention is especially useful in brakes and in clutchapplications. One aspect of the present invention relates to frictionmaterials which comprise a primary layer of a fibrous base materialcomprising less fibrillated aramid fibers, synthetic graphite, at leastone filler material and optionally other ingredients, and a secondarylayer comprising an optimum amount of carbon particles and at least oneretention aid. The carbon particles are deposited on the primary layerduring the process for making the fibrous base material.

The carbon particles are adhered to the surface of the fibrous basematerial with at least one retention aid. In preferred embodiments, thecarbon deposit fibrous base material of the present invention hassubstantially no loose carbon particles on the surface. The carbondeposit fibrous base material, when impregnated with a resin system,provides a friction material having high heat resistance and highfriction durability.

In a preferred method for making the carbon deposit fibrous basematerial, the carbon particles and the retention aid are combinedtogether and then deposited on the fibrous base material as a secondarylayer. In preferred embodiments, the carbon particles/retention aidsecondary layer is deposited at a thickness or depth of about 10 toabout 50 microns. In preferred embodiments, the retention aid is presentin amounts ranging from about 2 to about 25%, by weight, of the carbonparticles. In certain preferred embodiments, the retention aid comprisesa latex-type binder including, for example, acrylic nitride latex,neoprene latex and the like. In other preferred embodiments, theretention aid comprises at least one resinous material, including forexample, phenolic resins, epoxy resins and the like. In still otherpreferred embodiments, the retention aid comprises at least one sizingagent, including for example, epoxides, silanes and the like.

In preferred embodiments, the secondary layer comprises about 0.2 toabout 20%, more preferably about 5 to about 15%, and most preferablyabout 3 to about 5%, by weight, of the carbon particles, based on theweight of the fibrous base material. It has been found that carbonparticles having diameters ranging from about 0.5 to about 120 andpreferably from about 6 to about 50 microns.

The secondary layer comprising the carbon particles and retention aid ispresent at about 0.2 to about 20%, more preferably about 5 to about 15%,and most preferably about 3 to about 5%, by weight, based on the weightof the fibrous base material.

The area of coverage of the primary layer by the carbon particles in thesecondary layer is preferably in the range of about 3 to about 80% ofthe surface area of the primary layer. The primary layer of the fibrousbase is preferably porous and has an average pore diameter of about 2 toabout 15 microns, and in certain embodiments from about 2 to about 12microns. It has been found that the fibrous base material has, incertain embodiments, readily available air voids of at least about 50%

It has been found that an especially preferred primary layer of thefibrous base material comprises less fibrillated aramid fibers having afreeness greater than about 300-700 on the Canadian Standard Freenessindex, synthetic graphite, and optionally filler material. In certainembodiments, the less fibrillated aramid fibers have a freeness of about580 to about 640 on the Canadian Standard Freeness index. The length ofthe less fibrillated aramid fibers preferably ranges from about 3 toabout 6 mm in length. A preferred synthetic graphite is made bygraphitization of a graphite material at temperatures of about 280°-300°C. Preferably, the graphite has a diameter ranging from about 20 toabout 50 microns. In embodiments containing a filler material, it hasbeen found that diatomaceous earth is especially useful.

In especially preferred embodiments, the primary layer of the fibrousbase material comprises about 10 to about 50%, most preferably about 20to about 30%, by weight, less fibrillated aramid fibers; about 10 toabout 35%, most preferably about 15 to about 35%, by weight, syntheticgraphite; and about 20 to about 45%, most preferably about 20 to about30%, by weight, filler material. In especially preferred embodiments,the secondary layer comprises about 0.2 to about 20%, most preferablyabout 3 to about 5%, by weight, carbon particles and retention aid.

It has also been found, in certain embodiments, that the primary layerof the fibrous base material can include about 0 to about 40%, mostpreferably about 20 to about 40%, by weight, cotton fibers.

The fibrous base material can be impregnated using different resinsystems to form the friction material. In certain embodiments, it isuseful to impregnate the fibrous based material with a phenolic resin ora modified phenolic-based resin. In preferred embodiments, the frictionmaterial comprises about 25 to about 60% resin, by weight, based on theweight of the friction material. It has been found that one usefulmodified phenolic resin comprises an epoxy phenolic resin, where theepoxy resin present in the epoxy phenolic resin ranges from about 5 toabout 25 %, preferably about 10 to about 15%, by weight, based on theweight of the epoxy phenolic resin. It has also been discovered that, incertain embodiments, when a silicone resin is blended or mixed with aphenolic resin in compatible solvents and that silicone-phenolic resinblend is used to impregnate a fibrous base material of the presentinvention, a high energy friction material is formed. Such high energyfriction material has high friction stability and high heat resistance.

In certain embodiments, the amount of silicone resin in thephenolic-silicone mixture ranges from about 5 to about 80%, preferablyabout 15 to about 25% or about 20 to about 25%, by weight, based on theweight of the mixture. The mixture of phenolic and silicone resins ispreferably made by having the phenolic resin present in a first solventmaterial and the silicon resin present in a second solvent materialwhich is compatible with the first solvent material.

Another aspect of the present invention relates to a method for makingthe carbon deposit friction material. The less fibrillated aramidfibers, synthetic graphite and optionally filler material and/or cottonfibers are mixed together and dispensed, as the primary layer,preferably from a primary header box to form the fibrous base materialprimary layer. The carbon particles are mixed together with theretention aid and dispensed as the secondary layer, preferably from asecondary header box onto at least one surface of the primary layer. Thesecondary layer coats the primary layer to a preferred depth and amountof surface area coverage. The carbon deposit fibrous base material isimpregnated with at least one phenolic resin or modified phenolic resin.The impregnated carbon deposit fibrous base material is cured at adesired temperature for a desired period of time.

The carbon deposit friction material has higher heat resistance andhigher friction durability than other friction materials. The frictionmaterial of the present invention prevents uneven lining wear andtherefore the formation of separator plate "hot spots" from developingduring the useful life of the friction material. When there is littleuneven wear on the friction material, there is more likelihood tomaintain "steady state" of the clutch or brake components and therefore,more consistent performance of the clutch and brake. Further, thefriction material of the present invention shows good shear strengthsuch that the friction material resists delamination during use.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a scanning electron microphotograph of a fibrous basematerial impregnated with a silicone-phenolic blend (Example C).

FIG. 1B is a scanning electron microphotograph of a conventional fibrousmaterial impregnated with a phenolic resin (Conventional-1).

FIG. 2 is a thermal gravimetric analysis (TGA) graph showing therelationship between the percent of weight change and increasestemperatures for a fibrous base material impregnated with a phenolicresin (Example A) or a fibrous base material impregnated with asilicone-phenolic resin blend (Example B).

FIG. 3 is a TGA graph showing the percent of weight loss as temperaturesincrease, the change in the derivative weight (%/° C.), and the amountand percent of residue for Example A shown in FIG. 2.

FIG. 4 is a TGA graph showing the percent of weight loss as temperaturesincrease, the change in the derivative weight, and the amount andpercent of for Example B shown in FIG. 2.

FIG. 5 is a graph showing the stop time in seconds as the number ofcycles increases for a conventional material impregnated with abutadiene phenolic resin (Conventional-1) as compared to a fibrous basematerial impregnated with a silicone-phenolic resin blend (Example C)and a fibrous base material impregnated with different epoxy-phenolicresins (Example D 0.016 inch thin lining and Example F 0.020 inch thicklining).

FIG. 6 is a graph showing the ratio of static to dynamic coefficient offriction performance as the number of cycles increases for theConventional-1 material as compared to the Examples C, D and Fmaterials.

FIG. 7 is a graph showing the dynamic coefficient of frictionperformance as the number of cycles increases for the Conventional-1material as compared to the Examples C, D and F materials.

FIG. 8 is a graph showing the dynamic mid point coefficient frictionperformance as the number of cycles increases for the Conventional-1material as compared to Examples B, D and a fibrous base materialimpregnated with a different epoxy phenolic resin (Example E).

FIG. 9 is a graph showing the stop time performance as the number ofcycles increases for the Conventional-1 material as compared to theExamples B, D and E materials.

FIG. 10 is a graph showing high energy friction test cycles for aconventional material impregnated with a phenolic resin (Conventional-1)as compared to fibrous base material impregnated with an epoxy-phenolicresin (Example D).

FIG. 11 is a graph showing the high speed durability test at 7,000 rpm,0.3 LPM oil flow 1.5 kg-cm-sec² inertia showing the dynamic coefficientof friction as the number of cycles increases for a fibrous basefriction material impregnated with an epoxy-phenolic resin (Example D)and the Conventional-1 material and a conventional friction materialimpregnated with a phenolic resin (Conventional-2).

FIG. 12 is a graph showing the high energy durability test at 3,600 rpm,8.0 kg/cm² lining pressure, 5.0 kg-cm-sec² inertia showing the dynamiccoefficient of friction as the number of cycles increases for a ExampleD and the two conventional materials, Conventional-1 and Conventional-2.

FIG. 13 is a graph showing the engine dynamometer 4-3 down shiftdurability test, 2,000 cc IG/FE engine, 5,800 rpm showing the shift timein seconds for the 4-3 down shift engagements for the Example D and thetwo conventional friction materials, Conventional-1 and Conventional-2.

FIG. 14 is a graph comparing the shear strength (psi) for a fibrous basematerial impregnated with an epoxy-phenolic resin (Example E) and aconventional material (Conventional-2).

FIG. 15 is a graph showing the pore size (in microns) for a fibrous basematerial impregnated with an epoxy-phenolic resin (Example E) and aconventional material (Conventional-2).

FIG. 16 is a graph comparing the liquid permeability (cm² ×10⁻³) for afibrous base material impregnated with an epoxy-phenolic resin (ExampleE) and a conventional material (Conventional-2).

FIG. 17 is a graph showing the speed, torque, temperature and appliedpressure for Example E at an interface temperature of about 695° F. for500 cycles.

FIG. 18 is a graph showing the speed, torque, temperature and appliedpressure for Example E at an interface temperature of about 896° F. for10,500 cycles.

FIG. 19 is a graph showing the mid point dynamic coefficient of frictionfor Example E as the number of cycles increases.

FIG. 20 is a graph showing the high speed durability showing the midpoint coefficient of friction as the number of cycles increases forExamples C and E, as compared to the Conventional-1 material.

FIG. 21 is a graph showing a high speed durability at 6,000 rpm using anExxon 1975 fluid showing the static to dynamic coefficient of frictionratio as the number of cycles increases for Examples C and E, ascompared to the Conventional-1 material.

FIG. 22 is a graph showing a high speed durability test at 6,000 rpmusing an automatic transmission fluid JWS2318K showing the coefficientof friction as the number of cycles increases for Examples C, D and F,as compared to the Conventional-1 material.

FIG. 23 is a scanning electron microphotograph of a fibrous basematerial comprising about 45% less fibrillated aramid fibers (CSF about450-500), about 23% synthetic graphite, about 27% diatomaceous earth,and about 5% aramid fiber pulp (Example L).

FIG. 24 is a scanning electron microphotograph of a fibrous basematerial comprising about 45% less fibrillated aramid fibers (CSF about580-640), about 23% synthetic graphite, about 27% diatomaceous earth andabout 5% aramid fiber pulp (Example K).

FIG. 25 is a new separator plate profile having no carbon as a secondarylayer.

FIG. 26 is a separator plate surface profile for Example S having nocarbon as a secondary layer.

FIG. 27 is a separator plate surface profile for Example T having asecondary layer comprising about 5% carbon.

FIG. 28 is a separator plate surface profile for Example U having asecondary layer comprising about 10% carbon material.

FIG. 29 is a separator plate surface profile for Example V having asecondary layer comprising about 15% carbon material.

FIG. 30 is a separator plate surface profile for Example W having asecondary layer comprising about 20% carbon material.

FIG. 31 is a graph showing the percent of stop time change versus thesurface carbon coverage (area of percent) for Examples S, T, U, V and W,respectively.

FIG. 32 is a graph showing the percent of μd change versus surfacecarbon coverage (area of percent) for Examples S, T, U, V and W.

FIG. 33 is a graph showing the initial coefficient of friction change asthe cycles increase for Examples X, T and Y.

FIG. 34 is a graph showing the initial stop time in second versus cyclesfor Examples X, T and Y.

FIG. 35 is a graph showing a high energy durability test showing thestop time face for thousands of cycles for Examples Z, T and AA.

FIG. 36 is a graph showing the curve shape for Example X impregnatedwith a phenolic resin at 35% to 40% pick-up at level B at 70 cycles.

FIG. 37 is a graph showing the curve shape for Example X impregnatedwith a phenolic resin at 35% to 40% pick-up at level C at 95 cycles.

FIG. 38 is a graph showing the dynamic coefficient of friction forlevels A, B, C and D for Example X showing the initial, mid point andfinal coefficients of friction.

FIG. 39 is a graph showing the curve shape for Example T impregnatedwith a phenolic resin at 35% to 40% pick-up at level B at 70 cycles.

FIG. 40 is a graph showing the curve shape for Example T impregnatedwith a phenolic resin at 35% to 40% pick-up at level C at 95 cycles.

FIG. 41 is a graph showing the dynamic coefficient of friction forlevels A, B, C and D for Example T showing the initial, mid point andfinal coefficients of friction.

FIG. 42 is a schematic diagram showing one method for making a frictionmaterial according to the present invention.

FIG. 43 is a graph showing the percent of carbon particle loss comparedto the retention aid concentration in the secondary layer of the fibrousbase material, as based on the peel test.

BEST MODE OF CARRYING OUT THE INVENTION

Various resins useful in the present invention include phenolic resinsand phenolic-based resins. It is to be understood that variousphenolic-based resins which include in the resin blend other modifyingingredients, such as epoxy, butadiene, silicone, tung oil, benzene,cashew nut oil and the like, are contemplated as being useful with thepresent invention. In the phenolic-modified resins, the phenolic resinis generally present at about 50% or greater by weight (excluding anysolvents present) of the resin blend. However, it has been found thatfriction materials, in certain embodiments, can be improved when theimpregnant resin blend contains about 5 to about 80%, by weight, and forcertain purposes, about 15 to about 55%, and in certain embodimentsabout 15 to about 25%, by weight, of silicone resin based on the weightof the silicone-phenolic mixture (excluding solvents and otherprocessing acids).

Silicone resins useful in the present invention include, for example,thermal curing silicone sealants and silicone rubbers. Various siliconeresins are useful with the present invention. One resin, in particular,comprises xylene and acetylacetone (2,4-pentanedione). The siliconeresin has a boiling point of about 362° F. (183° C.), vapor pressure at68° F. mm, Hg: 21, vapor density (air=1) of 4.8, negligible solubilityin water, specific gravity of about 1.09, percent volatile, by weight,5% evaporation rate (ether=1), less than 0.1, flash point about 149° F.(65° C.) using the Pensky-Martens method. It is to be understood thatother silicone resins can be utilized with the present invention. Otheruseful resin blends include, for example, a suitable phenolic resincomprises (% by wt.): about 55 to about 60% phenolic resin; about 20 toabout 25% ethyl alcohol; about 10 to about 14% phenol; about 3 to about4% methyl alcohol; about 0.3 to about 0.8% formaldehyde; and, about 10to about 20% water. Another suitable phenolic-based resin comprises (%by wt.): about 50 to about 55% phenol/formaldehyde resin; about 0.5%formaldehyde; about 11% phenol; about 30 to about 35% isopropanol; and,about 1 to about 5% water.

It has also been found that another useful resin is an epoxy modifiedphenolic resin which contains about 5 to about 25 percent, by weight,and preferably about 10 to about 15 percent, by weight, of an epoxycompound with the remainder (excluding solvents and other processingaids) phenolic resin. The epoxy-phenolic resin compound provides, incertain embodiments, higher heat resistance to the friction materialthan the phenolic resin alone.

It further contemplated that other ingredients and processing aids knownto be useful in both preparing resin blends and in preparingimpregnating fibrous-based materials can be included in the frictionmaterials.

For the embodiments where a phenolic resin and silicone resin are used,no new compound is formed when the silicone resin and phenolic resin areblended together. Table 1 shows the prominent FT-IR peaks in wavenumbers for a cured silicone resin, a cured phenolic resin, and about50/50 blend of silicone resin and phenolic resin which has been cured.As can be seen, no new peaks occur in the 50/50 silicone-phenolic blend,and the peaks that are present reflect the presence of both the siliconeresin and the phenolic resin. Thus, it is shown that the resins cureseparately and that no new compound is formed.

                  TABLE 1    ______________________________________    PROMINENT FT-IR PEAKS IN WAVENUMBERS    SILICONE RESIN                  PHENOLIC RESIN                               50/50 BLEND    ______________________________________    --            3364         3366    2966          --           2964    --            1510         1510    --            1479         1481    1412          --           1410    1271          --           1261     798          --            800     767          --            769    ______________________________________

Both the silicone resin and the phenolic resin are present in solventswhich are compatible to each other. These resins are mixed together (inpreferred embodiments) to form a homogeneous blend and then used toimpregnate a fibrous base material. There is not the same effect if afibrous base material is impregnated with a phenolic resin and then asilicone resin is added thereafter or vice versa. There is also adifference between a mixture of a silicone-phenolic resin solution, andemulsions of silicone resin powder and/or phenolic resin powder. Whensilicone resins and phenolic resins are in solution they are not curedat all. In contrast, the powder particles of silicone resins andphenolic resins are partially cured. The partial cure of the siliconeresins and the phenolic resins inhibits a good impregnation of thefibrous base material.

Therefore, according to one aspect of the present invention, the fibrousbase material is impregnated with a blend of a silicone resin in asolvent which is compatible with the phenolic resin and its solvent. Inone embodiment, isopropanol has been found to be an especially suitablesolvent. It is to be understood, however, that various other suitablesolvents, such as ethanol, methyl-ethyl ketone, butanol, isopropanol,toluene and the like, can be utilized in the practice of this invention.According to the present invention, the presence of a silicone resin,when blended with a phenolic resin and used to impregnate a fibrous basematerial, causes the resulting friction materials to be more elasticthan fibrous base materials impregnated only with a phenolic resin. Whenpressures are applied to the silicone-phenolic resin blended impregnatedfriction material of the present invention, there is a more evendistribution of pressure which, in turn, reduces the likelihood ofuneven lining wear. After the silicone resin and phenolic resin aremixed together, the mixture is used to impregnate a fibrous basematerial.

Various methods for impregnating materials can be practiced with thepresent invention. The fibrous base material is impregnated with thephenolic or modified phenolic resin, preferably so that the impregnatingresin material comprises about 45 to about 65 parts, by weight, per 100parts, by weight, of the friction material. After the fibrous basematerial has been impregnated with the resin, the impregnated fibrousbase material is heated to a desired temperature for a predeterminedlength of time to form the friction material. The heating cures thephenolic resin at a temperature of about 300° F. When other resins arepresent, such as a silicone resin, the heating cures the silicone resinat a temperature of about 400° F. Thereafter, the impregnated and curedfriction material is adhered to the desired substrate by suitable means.

Another aspect of the present invention relates to a fibrous basematerial comprising less fibrillated aramid fibers, synthetic graphiteand at least one filler material, which are combined to form apaper-like fibrous base material. It is to be understood that variousmethods of forming fibrous base materials are contemplated as beinguseful in preparing the fibrous base material of the present invention.It has been found by the inventors herein that the use of lessfibrillated aramid fibers and synthetic graphite in a fibrous basematerial improves the friction material's ability to withstand hightemperatures.

While various friction lining materials disclose the use of aramidfibers, it has not been known until the present invention to provide afriction material comprising less fibrillated aramid fibers whichgenerally have few fibrils attached to a core fiber. The use of the lessfibrillated aramid fibers provides a friction material having a moreporous structure; i.e., there are more and larger pores than if atypical fibrillated aramid fiber is used. The porous structure isgenerally defined by the pore size and liquid permeability. In apreferred embodiment, the fibrous base material defines pores ranging inmean average size from about 2.0 to about 15 microns in diameter. Thelength of the less fibrillated fiber ranges from about 0.5 to about 6 mmand has a Canadian Standard Freeness (CSF) of greater than about 450 andin certain embodiments, about 500 to about 550 and in other certainembodiments, about 580-640 and most preferably about 620-640. Incontrast, more fibrillated fibers, such as aramid pulp, have a freenessof about 285-290.

The "Canadian Standard Freeness" (T227 om-85) means that the degree offibrillation of fibers can be described as the measurement of freenessof the fibers. The CSF test is an empirical procedure which gives anarbitrary measure of the rate at which suspension of three grams offibers in one liter of water may be drained. Therefore, the lessfibrillated aramid fibers have higher freeness or higher rate ofdrainage of fluid from the friction material than other aramid fibers orpulp. It has now been surprisingly found that friction materialscomprising the aramid fibers having a CSF ranging from about 530-650,preferably about 580-640, and most preferably about 620-640, providesuperior friction performance and have better material properties thanfriction materials containing conventionally more fibrillated aramidfibers. It has surprisingly been found that the longer fiber length,together with the high Canadian freeness, provide a friction materialwith high strength, high porosity and good wear resistance. As shown inthe examples below, high energy tests conducted with materialscontaining, for example, the less fibrillated aramid fibers (CSF about580-640 and most preferably about 620-640), have good long-termdurability and stable coefficients of friction.

The more porous the structure of the friction material, the moreefficient is the heat dissipation. The oil flow in and out of thefriction material during engagement of the friction material during useoccurs more rapidly when the friction material is porous.

It has further been discovered that the less fibrillated fibers,synthetic graphite and filler improve the pore structure of the fibrousbase material so that there are more porous openings throughout thefibrous base material. The increased porosity also increases theelasticity of the friction material. A lower degree of fibrillation ofthe less fibrillated aramid fibers results in a friction material havinga more porous structure.

It has not been known until the present invention to include syntheticgraphite in a fibrous base material comprising less fibrillated aramidfibers. The use of synthetic graphite in the fibrous base materialprovides a more three dimensional structure to the fibrous base materialthan other types of graphite material. The synthetic graphite is made bygraphitization of a raw stock material such as petroleum coke and a coaltar pitch binder. The raw materials are mixed and heated to temperaturesof about 2,800° to about 3,000° C. in special graphitizing furnaceswhich convert the baked carbon body into a polycrystaline graphitearticle. The synthetic graphite (which has high thermal conductivity)provides the friction material with the ability to dissipate heat morerapidly than other types of graphite. In certain embodiments, it ispreferred that the size and geometry of the synthetic graphite be in theabout 20 to about 50 micron size range. In these certain embodiments, ithas been discovered that if the graphite particle size is too large ortoo small, there is not the optimum three-dimensional structure andconsequently the heat resistance is not as optimum.

Various fillers are also used in the fibrous base material of thepresent invention. In particular, silica fillers, such as diatomaceousearth, are useful. However, it is contemplated that other types offillers are suitable for use in the present invention and that thechoice filler depends on the particular requirements of the frictionmaterial. Other ingredients can be added to the fibrous base material ofthe present invention, including for example, cotton fibers which can beadded to give the fibrous material higher coefficients of friction. Incertain embodiments, about 0 to about 20%, and in certain embodimentsabout 5 to about 15%, other filler such as aramid pulp and/or aramidfloc can also be added to the fibrous base material.

One example of a formulation for a fibrous base material comprises about10 to about 50%, by weight, of a less fibrillated aramid fiber; about 10to about 35%, by weight, of a synthetic graphite; and, about 20 to about45%, by weight, of a filler material. In certain embodiments, oneparticular formulation has found to be useful comprises about 45 toabout 50%, by weight, less fibrillated aramid fibers: about 15 to about25%, by weight, synthetic graphite; and, about 20 to about 30%, byweight, filler. Another useful formulation comprises about 20 to about30% less fibrillated aramid fibers, about 15 to about 25% syntheticgraphite, about 20 to about 30% filler material, and optionally about 0to about 40% cotton fibers. In further embodiments, the cotton fiberscan be present at about 20 to about 40%, by weight, or about 25 to about35%, by weight.

The following examples provide further evidence that the fibrous basematerial and friction material of the present invention are animprovement over the conventional friction material. Various preferredembodiments of the invention are described in the following examples,which however, are not intended to limit the scope of the invention.

Examples A and B both are a fibrous base material comprising about, inpercent, in weight, about 45% less fibrillated aramid fibers, about 23%synthetic graphite, about 27% diatomaceous earth filler, and about 5%optional filler comprising aramid pulp. Example A is impregnated with aphenolic material and Example B is impregnated with a silicone-phenolicresin blend comprising about 20% silicone and about 80% phenolic resins.

Example C is a fibrous base material comprising in percent, by weight,about 35% less fibrillated aramid fibers, about 25% synthetic graphite,about 25% diatomaceous earth filler material, and other optional fillersof about 5% aramid pulp and about 10% aramid floc, and impregnated witha silicone-phenolic resin blend.

Example D is a fibrous base material comprising in percent, by weight,about 25% less fibrillated aramid fibers, about 20% synthetic graphite,about 25% diatomaceous earth, and about 30% cotton fibers andimpregnated with a first epoxy-phenolic resin blend comprising about 10%epoxy and about 90% phenolic resins.

Example E is a fibrous base material comprising about 25% lessfibrillated aramid fibers, about 20% synthetic graphite, about 25%diatomaceous earth, and about 30% cotton fibers and impregnated with asecond epoxy-phenolic resin.

Example F is a fibrous base material comprising, in percent, by weight,about 25% less fibrillated aramid fibers, about 20% synthetic graphite,about 25% diatomaceous earth, and about 30% cotton fibers andimpregnated with the second epoxy-phenolic resin blend

EXAMPLE 1

FIG. 1A, shows a scanning electron microscopic (SEM) photograph ofExample C which indicates that a thin film of silicone resin formsbetween the fibers during impregnation. Example C has an increased poresize over friction materials impregnated with either a silicone resin orphenolic resin alone. Since the silicone resins and phenolic resins cureat different temperatures, the phenolic resin cures first while thesilicone resin cures later. A thin film of silicone resins formedbetween the fibers during cure. This thin film of silicone resin betweenthe fibers is thought to contribute to the high friction stability ofthe friction material. The film of silicone resin slows down thedeterioration of the friction material and allows the friction materialto have a high heat resistance at high temperatures.

The SEM photographs shown in FIG. 1A show a much larger pore structurethan for the phenolic resin-impregnated friction material, aconventional material (Conventional-1) which contains no lessfibrillated aramid fibers and no synthetic graphite, shown in FIG. 1B.

As seen in FIG. 1A, the blend of silicone and phenolic resins results ina fiber-resin interaction which creates a flexible and open fibernetwork. Up to about a 50% larger pore size has been seen with thephenolic-silicone blend impregnated friction material than over phenolicresin impregnated friction material alone. In certain embodiments, themean pore size ranges from about 2.5 to about 4 microns in diameter andthe friction material had readily available air voids of at least about50% and in certain embodiments at least about 60% or higher.

EXAMPLE 2

The capillary flow and permeability tests are shown in Table 2 below forExamples B, D, E and a comparative material having natural graphite butno synthetic graphite. The higher mean flow pore diameter and Darcy'spermeability indicate that the friction material is more likely to runcooler or with less heat generated in a transmission due to betterautomatic transmission fluid flow of material throughout the porousstructure of the friction material. During operation of a transmissionsystem, oil deposits on the surface of a friction material tend todevelop over time due to a breakdown of the automatic transmissionfluid, especially at high temperatures. The oil deposits on the fibersdecrease the pore openings. Therefore, when a friction materialinitially starts with larger pores, there are more open pores remainingduring the useful life of the friction material. In addition, thesilicone resin, due its elastic characteristics, allows the fibers inthe friction lining to have a more open structure.

                  TABLE 2    ______________________________________    CAPILLARY FLOW AND PERMEABILITY           Darcy's   Mean Flow  Sample Thickness           Permeability                     Pore Diameter                                Inches, cm    ______________________________________    Ex. B    2.0 × 10.sup.                         2.77 microns                                    0.021 0.05334    Ex. D    1.0 × 10.sup.-2                         2.85 microns                                    0.016 0.04191    Ex. E    1.0 × 10.sup.-2                         2.34 microns                                    0.017 0.04318    Compar.  5.1 × 10.sup.-3                         1.77 microns                                    0.019 0.04826    ______________________________________

EXAMPLE 3

Glaze analysis of the scanning electron microscopic photographs showsthat the silicone-phenolic resin blend has a slight fiber compression onthe surface while the phenolic resin alone has a pronounced fibercompression on the surface for unused plates. Further, as seen in Table3, in used plates, there are open pores remaining in a silicone-phenolicresin blend while there are very few pores open in the phenolic resinmaterial alone.

                  TABLE 3    ______________________________________    GLAZE ANALYSIS    SCANNING ELECTRON MICROSCOPY    UNUSED PLATES    Example C          Conventional Material - 1    ______________________________________    * Slight fiber compression                       * Pronounced fiber    on surface         compression on surface    * No fiber compression                       * No fiber compression    internally         internally    * Resin forms a film between                       * Resin only coats fibers    fibers    * Surface Glazes   * Surface glazes    * Open pores       * Very few open pores    ______________________________________

EXAMPLE 4

Previously, unreacted silicone resins have not been acceptable for usein a friction material since the silicone resin has low strength.However, it has now been found that the shear strength of thesilicone-phenolic resin blends is remarkably higher than for phenolicresins alone. The tensile shear test was run on the Instron tensiletester. A modified lap shear configuration was used with a 2 square incharea of friction material bonded on both side to steel plates. Thisassembly was then pulled until the paper sheared. The values in Table 4below indicate the internal shear strength of the paper under dryconditions at room temperature for Examples B, E and D.

The higher the shear strength, the better mechanical strength thefriction material has which means that more pressure is needed to shearthe friction lining.

                  TABLE 4    ______________________________________             Shear Strength PSI    ______________________________________    Ex. B      382.5               382.5    Ex. E      325.0               290.0    Ex. D      352.5               385.0    ______________________________________

EXAMPLE 5

The silicone-phenolic resin blend provides at least about a 50% increasein the "burn off" temperature of the friction material. This highfriction stability is an advantage over the currently available frictionmaterials. A thermal gravimetric analysis (TGA) shown in FIG. 2, whereinthe TGA curve shifts to higher temperatures, indicates increased heatresistance of the silicone-phenolic resin blend over the phenolicmaterial.

Both Examples A and B have improved heat resistance over conventionalmaterials and Example B is especially suitable for end-use frictionmaterial applications where heat resistance is a critical criterion.

FIGS. 3 and 4 compare the TGA graphs shown in FIG. 2, and the change inderivative weight (%/° C.) for the phenolic resin, Example A in FIG. 2(FIG. 3) and the silicone-phenolic blend, Example B in FIG. 2 (FIG. 4).The percent change in weight for the phenolic resin was 69.41% while thepercent change in weight for the silicone-phenolic blend was 61.87%. Asseen from FIGS. 3-4, the more rapid the weight loss, the less heatresistance the friction material possess.

EXAMPLE 6

FIG. 5 shows the stop time as the number of cycles increases for variousmaterials: Example C, D and F as compared to the Conventional-1 materialimpregnated with a butadiene-phenolic resin. The fibrous materials(Examples C, D and F) maintained a relatively uniform stop time, whilethe stop time for the conventional material rapidly rose to unacceptablelevels.

The ratio between the static coefficient of friction and the dynamiccoefficient of friction as the number of cycles increases was comparedfor Examples C, D and F and for the Conventional-1 material. As can beseen in FIG. 6, the fibrous base material impregnated withsilicone-phenolic blend material (Example C) performs consistentlybetter than the conventional material while the fibrous base materialimpregnated with epoxy-phenolic resins (Examples D and F) performedcomparatively well.

The dynamic coefficient of friction as the number of cycles increase wascompared for Examples C, D and F and for the conventional material(Conventional-1). FIG. 7 shows the dynamic coefficient of friction forthe friction materials (Examples C, D and F) remain relatively steady asthe number the cycles increased. Thus, the fibrous base materialsperform much better at a high speed than the conventional material. Itis important to note that there is no "fall off" of the coefficient offriction as the number of cycles increases for the fibrous basematerials.

A materials evaluation for a clutch run at 6,600 rpm (65 m/sec.),limited lubrication of 0.2 gpm was conducted for Examples B, D and E andfor the Conventional-1 material. The dynamic mid point coefficientgraphs of FIG. 8 shows that the conventional material was totallyunacceptable while the friction Examples B, D and E materials have arelatively steady coefficient of friction indicating that the system wasvery stable. As can be seen in FIG. 9, the stop time for theconventional material rapidly increased to unacceptable levels while thefriction materials (Examples B, D and E) maintained an acceptably shortstop time of about 0.52 to about 0.58 seconds throughout the test.

EXAMPLE 7

In certain embodiments, it is preferred that the target pick up of resinby the friction material range from about 40 to about 65%, and, incertain embodiments, about 60 to at least 65%, by weight, totalsilicone-phenolic resin. After the fibrous base material is impregnatedwith the resin, the fibrous base material is cured for a period of time(in certain embodiments for about 1/2 hour) at temperatures rangingbetween 300°-400° C. to cure the resin binder in the friction material.The final thickness of the friction material depends on the initialthickness of the fibrous base material and, in certain embodiments,preferably ranges from about 0.014" to about 0.040".

In Table 5 below, a friction material comprising the fibrous basematerial impregnated with about 60% resin pick up (P.U.) of asilicone-phenolic resin (Example C) was compared to a friction materialcomprising the same fibrous base material as in Example C butimpregnated with a phenolic resin with about 60% resin pick up (P.U.)(Example C-1) and to the Conventional-1 material impregnated with aphenolic resin with about 49% P.U. (Conventional-1). Assembly or coreplates were lined with friction materials impregnated with the testedresins to form a pack for testing. The dynamic coefficient of frictionremained steady (with a loss of only 5%) as the number of cyclesincreased for the silicone-phenolic resin friction materials. There wasno lining wear on the plates using the silicone-phenolic resin frictionmaterial. The lining condition of the silicone-phenolic resin blendfriction material remained good without breakouts, abrasion, or glazingoccurring. Further, the steel condition of the separator plates show nohot spots for the silicone-phenolic blend friction materials.

                  TABLE 5    ______________________________________    EFFECT OF RESIN CHANGE                CONV'L - 1   EX. C-1  EXAMPLE C    TEST RESIN %                49% P.U.     60% P.U. 60% P.U.    ______________________________________    LINING THICKNESS                0.016"       0.016"   0.016"    CYCLES                MID. DYNAMIC    75          0.135        0.134    0.134    3,000       0.121        0.123    0.130    6,000       0.118        0.113    0.127                STOP TIME SEC.    75          0.804        0.799    0.796    3,000       0.880        0.858    0.817    6,000       0.904        0.910    0.835    TORQUE CURVE                Decrease     Decrease Decrease    SHAPING.    LINING LOSS 0.0027"      0.0009"  No Loss    PER PLATE    LIVING CONDITION                Breakouts Heavy                             Abrasion Good                Glaze        Glaze    STEEL CONDITION                Distinct Hot Few Small                                      Light Heat                Spots        Hot Spots                                      Stains    ______________________________________

EXAMPLE 8

Table 6 below shows compression/relaxation studies done on an MTSmachine. This test reports the effect on paper caliper caused byrepeatedly pressing on a sample and releasing the sample through aseries of different pressures. These readings provide an indication ofthe internal resistance to set or compacting due to pressing. TheExample B material shows a greater elasticity than the comparativeexample described in Table 2 above. This greater elasticity allows formore uniform heat dissipation during use of the friction material sincethe fluid in the transmission or brake can rapidly move through theporous structure. Further, the increased elasticity provides moreuniform pressure or even pressure distribution on the friction materialsuch that uneven lining wear or separator plate "hot spots" areeliminated.

                  TABLE 6    ______________________________________    LOAD VS DEFLECTION    Compression/compression Set    Pressure    Psi           Example B    Compar.    ______________________________________     15 psi       .0000"/1 in. .0000"/1 in.                  .0000"       .0000"     50 psi       .0180"/1 in. .0104"/1 in.                  .0066"       .0034"     100 psi      .0348"/1 in. .0233"/1 in.                  .0083"       .0049"     200 psi      .0600"/1 in. .0419"/1 in.                  .0115"       .0070"     300 psi      .0805"/1 in. .0565"/1 in.                  .0123"       .0076"     400 psi      .0963"/1 in. .0658"/1 in.                  .0159"       .0070"     500 psi      .1112"/1 in. .0742"/1 in.                  .0188"       .0079"     700 psi      .1369"/1 in. .0939"/1 in.                  .0232"       .0111"     900 psi      .1533"/1 in. .1090"/1 in.                  .0242"       .0134"    1100 psi      .1703"/1 in. .1248"/1 in.                  .0267"       .0152"    1300 psi      .1922"/1 in. .1419"/1 in.                  .0324"       .0190"    1500 psi      .2179"/1 in. .1630"/1 in..                  .0404"       .0248"    ______________________________________

EXAMPLE 9

A friction material comprising less fibrillated aramid fibers andsynthetic graphite impregnated with an epoxy modified phenolic resin(Example D) and was compared to the conventional material(Conventional-1). A high speed friction cycles test is shown in FIG. 10,comparing the stroking test life and high energy friction test cycles.The friction material of the present invention performs better in allaspects than the conventional friction material.

FIG. 11 shows the results of a high speed durability test at 7,000 rpm,0.3 LPM oil flow with 1.5 kg-cm-sec² inertia. As the number of cyclesincreases, the dynamic coefficient of friction remained relativelyuniform for the friction material (Example D) while one conventionalmaterial (Conventional-2) failed at the beginning of the test and theperformance of another conventional material impregnated with aphenolic-based resin (Conventional-1) rapidly fell off after about 3,000cycles.

FIG. 12 shows the results of a high energy durability test at 3,600 rpm,8.0 kg/cm² lining pressure at 5.0 kg-cm-sec² inertia. The dynamiccoefficient of friction for the friction material (Example D) remainedremarkably steady throughout the entire durability test. In comparison,the conventional materials failed at an unacceptably short cycle ofusage life.

FIG. 13 shows the results of an engine dynamometer 4-3 down shiftdurability test for a 2,000 cc IG/FE engine at 5,800 rpm. As can beseen, the shift time in seconds for the 4-3 down shift engagements forthe friction material (Example D) remain relatively constant through atleast 40,000 down shift engagements. The conventional materials hadrapid increases in shift time at low shift engagement cycles.

EXAMPLE 10

The friction material of the present invention has high durability andhigh delamination resistance. The shear strength (psi) for the frictionmaterial of the present invention is greater than for the conventionalmaterials, as seen in FIG. 14. The use of the less fibrillated fibersand the resulting pore structure of the friction material providesincreased thermal resistance to the friction material. The fibergeometry not only provides increased thermal resistance, but alsoprovides delamination resistance and squeal resistance. The presence ofthe synthetic graphite particles and at least one filler material aidsin increasing the thermal resistance, maintaining a steady coefficientof friction, and increasing the squeal resistance.

EXAMPLE 11

The average pore size for the friction material of the present inventionas compared to the pore size of a conventionally resin impregnatedfriction material is shown in FIG. 15. The average pore size of thefriction lining of the present invention ranges from about 2.0 to about15 microns and is between about 20 to about 100% larger than for theconventional friction materials.

EXAMPLE 12

The liquid permeability for the friction material of the presentinvention was compared to a conventional material impregnated with aphenolic resin (Conventional-2). As seen in FIG. 16, the frictionmaterial of the present invention has about a 20% increase in liquidpermeability over the conventional materials.

EXAMPLE 13

FIG. 17 shows a friction material (Example D) comprising about 0.02"lining with about 44% pick up of a phenolic-epoxy resin at about 380° F.after 1/2 hour cure at an interface temperature of about 695° F. FIG. 17compares the speed, torque, temperature and applied pressure of thematerial run at 500 cycles showing the high friction stability of thefriction material of the present invention.

FIG. 18 shows the high friction stability of the friction material(Example D) comprising a 0.02" lining with about a 44% resin pick up ofanother phenolic-based resin cured at 380° F. for 1/2 hour, at aninterface temperature of 895° F. FIG. 18 shows the speed, torque,temperature and applied pressure of the material run for 10,500 cycles.

Table 7 below shows the mid point coefficient of friction for thefriction material (Example D) shown in FIGS. 17 and 18. The coefficientof friction remains relatively steady as the cycles increase, thusshowing the high friction stability of the friction material. Also, asshown in FIG. 19, the mid point dynamic coefficient of friction for theabove described friction materials in FIGS. 17 and 18 show that as thenumber of cycles increased, the mid point coefficient of frictionremained relatively steady. The torque curve shape shows that thefriction material of the present invention is especially useful in highspeed, high energy and high temperature applications. The total loss offriction material was only about 0.0077 inches and a loss per plate wasabout 0.0039 inches. The friction material showed a medium glaze and theseparator was only light heat stained, thus indicating a high qualityfriction material which is stable over a long period of time.

                  TABLE 7    ______________________________________    Example D                 MID    CYCLES       COEFFICIENT    ______________________________________     50          .132     100         .136     300         .135     500         .131     550         .131     600         .129     900         .124    1200         .122    1500         .121    2500         .121    4500         .122    6500         .121    8500         .123    10500        .126    ______________________________________

EXAMPLE 14

FIG. 20 shows a high speed durability test comparing a conventionalphenolic-based material impregnating a conventional friction lining toone embodiment of the friction material of the present materialimpregnated with a silicone-phenolic resin blend material (Example C)and another embodiment of the friction material of the present inventionimpregnated with a phenolic-epoxy resin material (Example D). Both thefriction materials of the present invention had more stable mid pointcoefficients of friction than the conventional friction material.

A high speed durability test run at 6,000 rpm was conducted comparingthe static to dynamic (S/D) coefficient of friction over a number ofincreasing cycles. As seen in FIG. 21, the conventional phenolicimpregnated friction material was compared to a silicone-phenolicimpregnated friction material of the present invention (Example C) andepoxy-phenolic impregnated friction material (Example E) of the presentinvention. The materials of the present invention have favorable staticto dynamic coefficient of friction ratios to the conventional material.

The coefficient of friction as cycles increase at 6,000 rpm was testedfor three samples of the fibrous base material of the present invention,each impregnated with a resin as follows: phenolic-epoxy impregnatedresin at a 0.016 inch thin fibrous base material (Example D),phenolic-based resin impregnated at 0.020 inch thick fibrous basematerial (Example F), and a silicone-phenolic resin (Example C). As seenin FIG. 22, these fibrous base materials impregnated with the variousresins compared favorably to a conventional friction material, whichperformed more poorly than each of the friction materials of the presentinvention.

The following further examples provide additional evidence that afibrous base material comprising at least one type of aramid fiberhaving a CSF of greater than about 530 preferably about 580-640 and mostpreferably about 620-640 is especially useful in friction materials.Such fibrous base materials are an improvement over other types offibrous base materials. Various comparative examples and variouspreferred embodiments are described in the following examples, whichhowever, are not intended to limit the scope of the invention. Each ofthe following examples, Comparative 3, Comparative 4 and Examples G, H,I and J is a formulation which is a fibrous base material comprising, inpercent, by weight, about 20% synthetic graphite, about 25% diatomaceousearth, about 30% cotton fibers, and varying types of fibers:

Comparative Ex. 3 about 25% epoxy coated aramid fibers (1 mm in length);

Comparative Ex. 4 about 25% epoxy coated aramid fibers (3mm in length);

Example G about 25% aramid fibers--CSF about 540;

Example H about 25% aramid fibers--CSF about 585;

Example I about 25% aramid fibers--CSF about 620-640; and

Example J about 25% aramid fibers--CSF about 450-500.

EXAMPLE 15

The mean pore diameter and Darcy's permeability for Comparative 3,Comparative 4 and Examples G, H and I are shown in Table 8 below forboth resin saturated fibrous base materials and for raw papers(unsaturated).

The higher mean flow pore diameter indicates that the friction materialis more likely to have lower interface temperature with more efficientheat dissipation in a transmission due to better automatic transmissionfluid flow of material throughout the porous structure of the frictionmaterial. During operation of a transmission system, oil deposits on thesurface of a friction material tend to develop over time due to abreakdown of automatic transmission fluid, especially at hightemperatures. The oil deposits on the fibers decrease the pore openings.Therefore, when a friction material initially starts with larger pores,there are more open pores remaining during the useful life of thefriction material. It is noted that Example I (comprising lessfibrillated aramid fibers (CSF about 620-640)) has especially desirablemean pore diameters.

                  TABLE 8    ______________________________________              Bond              Cond.        Pore              Time/min.    Mean      L-Prem    Paper     Temp °F.                           Pore      Darcy    ID        FLT/in.      Dia. (μm)                                     Const.    ______________________________________    Compar. 3 0.017        15.1      0.23    Compar. 4 0.017        23.9      0.26    Ex. G     0.017        4.3       0.04    Ex. H     0.017        5.4       0.04    Ex. I     0.017        7.0       0.12    RAW PAPER    Compar. 3          25.9      0.50    Compar. 4          26.3      0.64    Ex. G              5.5       0.06    Ex. H              6.0       0.11    Ex. I              7.8       0.12    ______________________________________

EXAMPLE 16

Table 9 below indicates the compression, compression set and shearstrength values for the Comparative 3, Comparative 4 and Examples G, Hand I. It is to be especially noted that Examples G, H and I haveacceptable compression and compression set values and further that theshear strength is much greater than Comparatives 3 and 4.

                  TABLE 9    ______________________________________    Friction                        Shear    Material  Comp.       Comp. Set Strength    ID        in./in.     in./in.   psi    ______________________________________              100 psi     100 psi   A              300 psi     300 psi   B              700 psi     700 psi   C              1500 psi    1500 psi  Avg.    Compar. 3 0.0608      0.0141    128              0.1222      0.0232    126              0.1847      0.0426    126              0.2999      0.1049    127    Compar. 4 0.0771      0.0188    83              0.1448      0.0309    89              0.2078      0.0488    90              0.2955      0.0821    87    Ex. G     0.0157      -0.0005   364              0.0475      0.0002    357              0.0943      0.0108    341              0.1946      0.0510    354    Ex. H     0.0206      0.0017    313              0.0528      0.0030    325              0.0978      0.0118    317              0.1721      0.0414    318    Ex. I     0.0196      0.0000    332              0.0546      0.0015    349              0.1119      0.0110    336              0.2321      0.0482    339    ______________________________________

EXAMPLE 17

The Table 10 shows improved heat resistance over comparative examplesand contains data showing the TMA, the differential scanning calorimeter(DSC) and thermal gravimetric analysis (TGA) data for the comparatives 3and 4 and Examples G, H and I.

                                      TABLE 10    __________________________________________________________________________                   TGA-Total                         TGA-Top                               TGA-Mid.                                     TGA-Bot.                   %/Temp. °C.                         %/Temp. °C.                               %/Temp. °C.                                     %/Temp. °C.         TMA  DSC  1st Peak                         1st Peak                               1st Peak                                     1st Peak         Alpha              Onset °C.                   2nd Peak                         2nd Peak                               2nd Peak                                     2nd Peak    Paper         Onset °C.              Peak °C.                   3rd Peak                         3rd Peak                               3rd Peak                                     3rd Peak    ID   % Expan              J/G  Residue                         Residue                               Residue                                     Residue    __________________________________________________________________________    Compar. 3         650  190  18.81 19.40 20.67 20.64         90   218  52.65 51.56 50.04 56.70         4.9% 5.00 13.05 10.42 11.47 6.61                   16.28 19.23 18.63 16.88    Compar. 4         1300 186  18.87 19.62 18.20 18.63         108  236  56.26 62.25 56.63 58.85         8.9% 5.04 13.10 5.74  11.80 9.53                   12.79 13.65 14.43 15.61    Ex. G         525  190  17.99 18.38 18.42 17.79         73   205  55.88 55.27 54.37 57.41         4.6% 1.51 11.65 10.89 11.44 8.16                   15.07 15.91 16.34 16.47    Ex. H         558  190  19.48 19.28 20.33 19.79         84   205  52.17 51.30 51.04 53.28         4.2% 2.51 12.34 13.06 11.88 9.49                   16.76 17.03 17.40 18.03    Ex. I         672  205  19.62 19.09 19.64 18.57         86   225  53.66 56.25 52.21 52.19         5.2% 0.11 11.65 8.41  11.81 13.80                   16.02 16.36 16.80 15.08    __________________________________________________________________________

Table 11 provides a summary of test procedure conditions for the highspeed durability tests 5004C and 5004A, the breaking characteristic test5004D, the high energy durability tests 5003A and 5030C, and the μ-v-p-tcharacteristic test 5010A for the materials shown in Examples 18-23below.

                  TABLE 11    ______________________________________                              Break-In    Test Procedure            Characteristic    ______________________________________            High Speed Durability Test              5004C       5004A       5004D    ______________________________________    Level     Level A & C Level A & C Level A    Cycles    50 cycles   ←      200 cycles    Speed     3700 rpm    ←      ←    Inertia   2.17 kg cm.sec.sup.2                          ←      ←    Pressure  137.8 KPa   ←      ←    Temperature              100-100° C.                          ←      ←    Oil flow  0.757 lpm   ←      ←    Kinetic energy              15122 Joule ←      ←    Level     Level B     Level B     --    Cycles    5000 cycles 2000 cycles --    Speed     6200 rpm    ←      --    Inertia   1.70 kg cm sec.sup.2                          ←      --    Pressure  --          --          --    Stop Time *0.8 sec.   ←      --    Temperature              115-120° C.                          110-110° C.                                      --    Oil flow  0.787 lpm   ←      --    Kinetic energy              35720 Joule --    Power density              1.98 W/mm.sup.2                          ←      --    ______________________________________            High Energy            Durability Test              5003C       5030C       5010A    ______________________________________    Level     Level A & C Level A & C Level A    Cycles    50 cycles   ←      200 cycles    Speed     3600 rpm    ←      800 rpm    Inertia   1.70 kg cm sec.sup.2                          ←      3.553                                      kg cm sec.sup.2    Pressure  137.8 kPa   ←      59.27 kPa    Temperature              97-103° C.                          ←      ←    Oil flow  0.757 lpm   ←      ←    Kinetic energy              15127 Joule ←      1223 Joule    Level     Level B     Level B     Level B    Cycles    2000 cycles 5000 cycles 200 cycles    Speed     3600 rpm    4000 rpm    3600 rpm    Inertia   7.48 kg cm sec.sup.2                          5.00 kg cm sec.sup.2                                      3.553                                      kg cm sec.sup.2    Pressure  --          --          355.6 kPa    Stop Time **0.8 sec.  ***0.95 sec.                                      --    Temperature              97-103° C.                          115-120° C.                                      97-103° C.    Oil flow  0.787 lpm   ←      ←    Kinetic energy              52124 Joule 43016 Joule 24761 Joule    Power density              2.89 W/mm.sup.2                          2.01 W/m.sup.2                                      --    ______________________________________     Note:     *In level B, adjust apply pressure to maintain 0.8 seconds stop time     within the first 10 cycles.     **In level B, adjust apply pressure to maintain 0.8 seconds stop time     within the first 10 cycles.     ***In level B, press start at 140 kPa, adjust the pressure to maintain     0.95 seconds stop time by 90th cycle.

EXAMPLE 18

In the Table 12 below, the high speed durability is shown for theComparatives 3 and 4 and Examples G, H, I and J. The friction materialwas impregnated with an epoxy modified phenolic resin at about 37%pickup. The shear strength of the Examples G, H and I were comparable toExample J. The compression and compression set showing the strain showsacceptable strength and elasticity which allows for more uniform heatdissipation during use of the friction material since the fluid in thetransmission or brake can rapidly move through the porous structure. Theincreased elasticity also provides more uniform pressure or evenpressure distribution on the friction material such that uneven liningwear or separator plate "hot spots" are eliminated or minimized.

Table 13 below shows high speed durability testing showing the frictionplate condition, separator plate condition and the overall condition ofeach sample. It is to be especially noted that Example I only had lightglazing and pitting and the overall condition was fair with no materialloss.

Table 14 below shows the high speed durability test showing the frictioncoefficient at energy levels A, B and C, the stop-time and the percentof fade. The Comparative 4, Example G and J experienced a break-out andthe test was stopped. The fibrous base material in Examples H and Iperformed well at high speeds. It is important to note that there is no"fall off" of the coefficient of friction as the number of cycleincreases for the fibrous base material in Example I.

                  TABLE 12    ______________________________________    High Speed Durability Test    (Procedure 5004A)             Comp.   Comp.    Material 3       4       Ex. G Ex. H Ex. I Ex. J    ______________________________________    Raw paper             25.86   26.29   5.46  6.00  7.84  --    pore size (μm)    permeability             0.516   0.653   0.077 0.115 0.127 --    (cm.sup.2)    Resin 37% p/u             15.09   23.90   4.32  5.35  7.04  9.88    pore size (μm)    permeability             0.225   0.295   0.030 0.054 0.115 --    (cm.sup.2)    Shear strength             127.2   87.9    354.6 318.8 339.5 359.8    (psi)    300 psi comp/             0.1222/ 0.1448/ 0.0475/                                   0.0528/                                         0.0546/                                               0.0698/    set    (strain) 0.0232  0.0309  0.0002                                   0.0030                                         0.0015                                               0.0106    1500 psi comp/             0.2999/ 0.2955/ 0.1946/                                   0.1721/                                         0.2321/                                               0.1988/    set    (strain) 0.1049  0.0821  0.0510                                   0.0414                                         0.0482                                               0.0362    ______________________________________

                                      TABLE 13    __________________________________________________________________________    High Speed Durability Test    (Procedure 5004A)    Friction    Tests  Comp. 3                 Comp. 4                       Ex. G Ex. H                                  Ex. I Ex. J    __________________________________________________________________________    Total wear           0.0168                 impossible                       impossible                             0.0269                                  0.0081                                        impossible    (inch)    Friction plate           light heavy heavy glazing                                  glazing                                        heavy    condition           glazing &                 material loss                       material loss                             pitting                                  light pitting                                        material loss           pitting           breakout    Seperator           dark heat                 heat stain                       heat stain                             heat stain                                  heat stalight                                        heat stains    plate  stain hot spots   hot spots                                  hot spots    condition    Overall           poor  not complete                       not complete                             fair fair  poor    condition    __________________________________________________________________________

                  TABLE 14    ______________________________________    High Speed Durability Test    (Procedure 5004A)    Friction    Coeffi-    cients Comp. 3  Comp. 4  Ex. G  Ex. H                                         Ex. I                                              Ex. J    ______________________________________    Level A    (50    cycles)    μs  0.092    0.099    0.099  0.101                                         0.095                                              0.103    μi  0.153    0.173    0.141  0.152                                         0.129                                              0.161    μd  0.130    0.132    0.136  0.136                                         0.128                                              0.141    μO  0.141    0.134    0.149  0.147                                         0.133                                              0.145    μO/μd           1.085    1.015    1.095  1.081                                         1.039                                              1.028    Level B    (2050    cycles)    μs  0.071    787 cycles                             592 cycles                                    0.086                                         0.081                                              101 cycles    μi  0.127    break-out                             break-out                                    0.133                                         0.136                                              break-out    μd  0.127    stop     stop   0.124                                         0.126                                              stop    μO  0.122                    0.128                                         0.124    μO/μd           0.961                    1.032                                         0.984    Level C    (2100    cycles)    μs  0.106    --       --     0.102                                         0.101                                              --    μi  0.163    --       --     0.161                                         0.160                                              --    μd  0.148    --       --     0.146                                         0.148                                              --    μO  0.149    --       --     0.141                                         0.149                                              --    μO/μd           1.007    --       --     0.966                                         1.007                                              --    Stop-time    (sec)    A      0.916    0.917    0.917  0.891                                         0.958                                              0.855    B      0.803    --       --     0.814                                         0.792                                              --    C      0.805    --       --     0.856                                         0.835                                              --    Fade % μd           -0.8     --       --     -5.3 -3.8 --    stop time           +0.1     --       --     -0.2 +0.6 --    ______________________________________

EXAMPLE 19

The high energy durability tests are shown in Tables 15, 16 and 17 belowfor the Comparatives 3 and 4 and Examples G, H, I and J impregnated withthe epoxy modified phenolic resin. It is noted that the amount of resinpick-up varies for different examples. In Table 15, the compression andcompression set data show acceptable values for the Examples G, H, I andJ.

Table 16 shows the friction plate condition, the separator platecondition and the overall condition. It is to be noted that Example Ishowed only a slight abrasion, glazing and pitting and that theseparator plate had few hot spots or heat strains.

Table 17 below shows the friction coefficient for levels A, B and C, thestop time and percent rate. As can be seen, the examples of the presentinvention perform consistently better than the comparative materials.Thus, the fibrous base materials of the present invention performed muchbetter at higher speeds than the comparative materials. It is alsoimportant to note that there is no fall off of coefficient of frictionas the number of cycles increases for the fibrous base materials ofExample I. Also, the relatively steady coefficient of friction indicatesthe friction materials are very stable.

                                      TABLE 15    __________________________________________________________________________    High Energy Durability Test    (Procedure 5003A)    Material Comp. 3                   Comp. 4                         Ex. G                              Ex. H                                   Ex. I                                        Ex. J    __________________________________________________________________________    Raw paper             25.86 26.29 5.46 6.00 7.84 --    pore size (μm)    permeability (cm.sup.2)             0.516 0.653 0.077                              0.115                                   0.127                                        --    resin 37% p/u             20.03 22.44 4.32 5.35 7.04 9.33    pore size (μm)             (53.2% pu)                   (54.9% pu)                         (37% pu)                              (35% pu)                                   (37% pu)    permeability (cm.sup.2)             --    --    0.030                              0.054                                   0.115                                        --    Shear strength (psi)             224.2 177.9 354.6                              318.8                                   339.5                                        359.8    300 psi comp/set             0.1016/                   0.1563/                         0.0475/                              0.0528/                                   0.0546/                                        0.0698/    (strain) 0.0122                   0.0323                         0.002                              0.0030                                   0.0015                                        0.0106    1500 psi comp/set             0.2886/                   0.3746/                         0.1946/                              0.1721/                                   0.2321/                                        0.1988/    (strain) 0.0627                   0.0934                         0.0510                              0.0414                                   0.0482                                        0.0362    __________________________________________________________________________

                                      TABLE 16    __________________________________________________________________________    High Speed Durability Test    (Procedure 5003A)    Friction    Test   Comp. 3                  Comp. 4                         Ex. G Ex. H  Ex. I  Ex. J    __________________________________________________________________________    Total wear           0.0205 0.0245 impossible                               0.0242 0.0256 0.0192    (inch)    Friction plate           light glazing &                  glazing                         heavy heavy glaze &                                      glazing                                             glazing    condition           pitting                  light pitting                         material loss                               abrasions                                      abrasion                                             abrasion                               breakout                                      slight pitting    Seperator           heat stain                  heat stain                         heat stain                               mid wear                                      mid wear                                             heat stained    plate  few hot spots                  few hot spots                         hot spots                               mark & heat                                      mark few hot                                             hot spots    condition                  stains heavy                                      spots heat                               abrasion                                      stains    Overall           fair 1 fair 2 not complete                               poor   fair 2 fair    condition    __________________________________________________________________________

                  TABLE 17    ______________________________________    High Energy Durability Test    (Procedure 5003A)    Friction   Comp.   Comp.    Coefficients               3       4       Ex. G Ex. H                                          Ex. I Ex. J    ______________________________________    Level A           μs   0.102   0.103 0.111 0.101                                            0.104 0.121    (5O    μi   (0.141) (0.240)                                 0.145 0.148                                            (0.137)                                                  0.146    cyles) μd   0.131   0.124 0.141 0.131                                            0.130 0.136           μO   0.142   0.136 0.145 0.143                                            0.140 0.149           μO/μd                   1.084   1.097 1.028 1.091                                            1.0777                                                  1.096    Level B           μs   0.101   0.101 124   0.093                                            0.103 0.097                                 cycles    (2O5O  μi   0.137   0.129 break-                                       0.127                                            0.128 0.141                                 out    cycles)           μd   0.137   0.129 stop  0.128                                            0.130 0.132           μO   0.142   0.123       0.131                                            0.128 0.146           μO/μd                   1.036   0.953       1.023                                            0.985 0.106    Level C           μs   0.115   0.114 --    0.100                                            0.108 0.103    (21OO  μi   0.174   0.160 --    0.152                                            0.154 0.173    cycles)           μd   0.152   0.151 --    0.145                                            0.150 0.149           μO   0.152   0.155 --    0.142                                            0.150 0.144           μO/μd                   1.000   1.026 --    0.979                                            1.000 0.966    Stop-time           A       0.867   0.913 0.863 0.878                                            0.888 0.840    (sec)  B       0.756   0.778 --    0.816                                            0.807 0.773           C       0.800   0.812 --    0.841                                            0.843 0.830    Fade % μd   +3.0    -0.8  --    -4.5 -3.0  -2.2    stop time      -5.7    -2.5  --    +1.7 +1.4  -4.0    ______________________________________

EXAMPLE 20

High energy durability tests were also conducted for Examples I and Jusing different resins and different percentages of resins. It is to benoted that the shear strengths vary slightly with the type of resin, butthat the shear strengths are consistently acceptable. The compressionand compression set data indicate a better performance by Example I overthe Example J. The coefficient of friction levels, for example, I isimpregnated with a phenolic resin which shows better results than theother tested examples. Again, there is no "fall off" shown for Example Iin Table 18.

                                      TABLE 18    __________________________________________________________________________    High Energy Durability Test    (Procedure 5030A)             Ex. I Ex. J  Ex. I  Ex. J    __________________________________________________________________________    Resin    phenolic                   phenolic                          epoxy-modified                                 epoxy-modified                          phenolic                                 phenolic    Pick-up  35%   36%    39.7%  40.7%    Shear psi             340   356    254    301    Comp/comp-set             0.050/0.006                   0.053/0.008                          0.066/0.015                                 0.059/0.008    300psi/1500psi             0.147/0.016                   0.192/0.036                          0.217/0.047                                 0.220/0.049    Total wear (in.)             0.0106                   0.0142 --     --    Level A           μs             0.094 0.097  0.095  0.109/0.092    50 cycles           μi             0.132 0.130  0.131  0.157/0.146           μd             0.132 0.132  0.121  0.129/0.120           μO             0.140 0.136  0.133  0.144/0.136    Level B           μs             0.077 Stopped test at                          Failed at 110                                 Failed at    5050 cycles           μl             0.102 3378 cycles                          cycles 100 & 125 cycles           μd             0.101 Stop-time           μO             0.113 1.244 sec.    Level C           μs             0.103 --     --     --    5100 cycles           μi             0.147 --     --     --           μd             0.120 --     --     --           μO             0.139 --     --     --    Stop-time           A 0.825 0.861  0.916  08.54/0.927    (sec.) B 1.109 --     --     --           C 0.923 --     --     --    Stop-time Fade             4000 cycles                   2100 cycles                          --     --    15% cycles    __________________________________________________________________________

In the Examples 21-23 below, each of the following fibrous basematerials is a formulation which comprises, in percent, by weight, about23% synthetic graphite, about 27% diatomaceous earth, about 5% aramidfiber pulp and varying types of fibers:

Example K about 45% aramid fibers--(CSF between 580-640);

Example L about 45% aramid fibers--(CSF between about 450-500);

Example M about 45% aramid fibers--(CSF between about 580-640);

Example N about 45% aramid fibers--(CSF between about 450-500); and

EXAMPLE O about 45% aramid fibers--(CSF between about 580-640).

EXAMPLE 21

Examples K and L shown in Table 19 below were saturated with about 48%and 46%, pick-up, respectively, with a resin blend of 50% silicone andabout 50% phenolic resin. The shear strength and the compression andcompression set data show that Example K comprising the less fibrillatedaramid fibers (CSF 580-640) is comparable to Example L. The TGA, DSC andTMA data for Example K show high friction stability and good heatresistance.

FIG. 23 shows the pore size of Example L, while FIG. 24 shows the poresize for Example K.

                  TABLE 19    ______________________________________                 Ex. K      Ex. L    ______________________________________    Resin % PU     48% PU       46% PU    Raw paper      6.00         6.28    pore size (μm)    Graphite       1.3/2.8      2.4/5.1    concentration    Felt/wire (%)    Saturated paper                   5.99         5.20    pore size (μm)    shear strength 313          422    (psi)    Comp/Comp-set  0.074/0.016  0.059/0.008    (strain)       0.210/0.042  0.172/0.027    300/1500 psi    TGA            21.78%       22.08%    Residue        581.7° C.                                597.8° C.    Peak Temp.    DSC            247.44       243.02    Peak °C.                   27.68        26.38    J/g    TMA            561          439    α        292          276    Peak °C.    ______________________________________

EXAMPLE 22

The high speed durability test under Procedure 5004C for Examples K, L,M and N are shown in Tables 20 and 21 below. The friction platecondition showed only medium to light glaze and the separator platecondition showed medium heat stains for the fibrous base materialcontaining less fibrillated aramid fibers (CSF about 580-640). Thecoefficient of friction for levels A, B and C indicate that the fibrousbase materials perform consistently. The stop time and percent fade wasabout 3 to 4 times better for Exhibit K than for Exhibit L. The stoptime for Exhibit M was at least about 4 times better than for Exhibit N,and the percent fade was more than two times better for Exhibit M thanfor Exhibit N.

                  TABLE 20    ______________________________________    High Speed Durability Test    (Procedure 5004C)                 Ex. K       Ex. L    ______________________________________    Resin              48% PU        46% PU    Total wear (in.)   0.0056        0.0068    Friction plate     Medium glaze  Light to Medium    condition                        glaze    Separator plate    Medium heat stains                                     Medium to heavy    condition                        heat stains    Level A     μS  0.095         0.104    50 cycles   μi  0.135         (0.146)                μd  0.119         0.129                μO  0.123         0.132    Level B     μS  0.095         0.094    5050 cycles μi  0.116         0.110                μd  0.115         0.112                μO  0.122         0.121    Level C     μS  0.115         0.113    5100 cycles μi  0.137         0.134                μd  0.122         0.116                μO  0.129         0.123    Stop-time   A      0.946         0.885    (sec.)      B      0.827         0.914                C      0.932         0.957    Stop-time fade     3.5%          12.8%    μd fade (%)     5.7%          14.5%    ______________________________________

                  TABLE 21    ______________________________________    High Speed Durability Test    (Procedure 5004C)               Ex. M       Ex. N    ______________________________________    Resin            41% PU        42% PU    Total wear (in.) 0.0077        0.0069    Friction plate   Medium glaze  Medium glazing &    condition                      abrasion    Separator plate  Medium heat stains                                   Medium heat    condition        hot spots, light                                   stains hot spots                     abrasion    Level A   μS  0.095         0.095    50 cycles μi  0.148         0.153              μd  0.118         0.119              μO  0.121         0.123    Level B   μS  0.086         0.084    5050 cycles              μi  0.112         0.113              μd  0.110         0.112              μO  0.119         0.118    Level C   μS  0.109         0.105    5100 cycles              μi  0.145         0.143              μd  0.119         0.122              μO  0.126         0.126    Stop-time A      0.965         0.922    (sec.)    B      0.829         0.881              C      0.938         0.924    Stop-time fade   1.6%          7.6%    μd fade (%)   5.2%          11.8%    ______________________________________

EXAMPLE 23

The break-in characteristics are shown in Table 22 below for Examples K,L and 0. The break-in characteristics indicate good behavioralcharacteristics and low wear.

                  TABLE 22    ______________________________________    Break-In Characteristic Test    (Procedure 5004D)                       48% PU 46% PU    Type of Fiber    Ex. K     Ex. Q    Ex. L    ______________________________________    1 cycles    μS    0.092     0.104  0.117                μi    0.106     0.117  0.127                μd    0.092     0.108  0.114                μO    0.096     0.103  0.111    50 cycles   μS    0.102     0.098  0.099                μi    0.143     0.142  0.161                μd    0.116     0.115  0.133                μO    0.121     0.118  0.131    200 cycles  μS    0.097     0.097  0.105                μi    0.146     0.145  0.160                μd    0.123     0.123  0.142                μO    0.128     0.122  0.139    Stop-time   1        1.104     1.093  1.015    (sec.)      50       0.962     0.988  0.868                200      0.919     0.946  0.828    Total Wear           0.0011    0.001  0.0012    (in.)    ______________________________________

The Examples 15-23 show that increase in Canadian Standard Freeness ofaramid type fibers produces fibrous base materials having improveddurability. Further, fibrous base materials containing aramid fibershaving a CSF of at least about 580-640, and preferably about 600-640 andmost preferably about 620-640, have larger pore sizes than other typesof aramid fibers. The high inertia durability of the fibrous basematerials having such less fibrillated aramid fibers is improved andthere is a better fade resistance.

In another aspect of the present invention, friction materialscomprising a two layer fibrous base material and impregnated with asuitable phenolic, epoxy modified phenolic, or phenolic/silicone blendresin provides superior friction performance and better break-incharacteristics than friction materials containing conventionalmaterials. The fibrous base material comprises a primary layer of a lessfibrillated aramid fiber, synthetic graphite, filler materials such asdiatomaceous earth, and in certain embodiments, cotton and/or aramidpulp and other optional ingredients. The secondary layer comprises adeposit of carbon particles on the surface of the fibrous materialduring the fibrous base material making process.

The adhesion of the carbon particles on the surface of the fibrous basematerial can be improved by using retention aids and/or binding agentssuch as a suitable amount of latex type materials present in the primaryor lower layer. In certain embodiments, it has been found useful to haveabout 1 to about 5% and preferably about 2%, by weight, of the latexbinding agent present in the primary layer.

The uniformity of the layer of carbon particles on the surface offibrous base materials can also be improved using a range and size ofthe carbon particles that is preferably from about 0.5 to about 80 μm.However, it is contemplated that other sizes of carbon particles arealso useful as a secondary layer on the fibrous base material of thepresent invention.

One preferred embodiment for making a friction material 10 using acarbon coated fibrous 12 base material of the present invention is shownin FIG. 42. The fibrous base material 12 comprises a lower layer 14having an upper or top surface 16 and a lower or bottom surface 18. In apreferred embodiment the lower layer 14 comprises the less fibrillatedaramid fiber, synthetic graphite, filler material, optionally cottonand/or aramid pulp. While the lower layer 14 is wet, carbon particles 20are deposited onto the top surface 16 of the wet lower layer 14. Incertain embodiments, the lower layer 14 further comprises a suitableamount of at least one type of binder material such that the carbonparticles are adhered to the wet layer 14 by the binder material whichis present in the lower wet layer 14. Suitable binder materials include,for example a latex type binder material and/or an alum based materialhaving a pH of about 4.5 or less.

In yet another preferred embodiment, the carbon particles 20 andretention aid 22 are mixed together and dispersed or deposited onto thetop surface 16 of the lower layer 14.

In another embodiment it is also useful to use a low vacuum pressuremeans 30 on a lower side of the wet layer 14 prior to deposition of thecarbon particles 20 and retention aid 22 on the opposing bottom surface18 of the layer 14.

In a preferred embodiments the amount of carbon particles range fromabout 0.2 to about 20%, by weight, and in certain embodiments about 15to about 5%, by weight, and in other embodiments about 2 to about 20%,by weight, of the friction paper. In preferred embodiments the area ofcoverage of carbon particles on the primary layer surface is in therange of the about 3 to about 90% of the surface area.

A preferred process for producing the non-asbestos friction materialcomprises mixing less fibrillated aramid fibers with synthetic graphicand at least one filler to form a fibrous base material. At least onesurface of the fibrous base material is coated with the carbon particlesand retention aid. The fibrous base material coated with the carbonparticles and retention aid is impregnated with at least one phenolic ormodified phenolic resin. The impregnated, coated fibrous base materialis cured at a predetermined temperature for a predetermined period oftime.

In another embodiment a phenolic resin can be mixed with a siliconeresin to impregnate the fibrous base material, as disclosed inco-pending patent application Ser. No.08/126,000, filed Sep. 23, 1993.The entire contents of which are expressly incorporated by referenceherein.

It has been found that the longer fiber length, together with the highCanadian freeness and layer of carbon particles provides a frictionmaterial which provides high durability, good wear resistance andimproved break-in characteristics. As shown in the examples below, thechange in the coefficient of friction of the carbon deposit layeredfriction material in the initial stages is much less than frictionmaterials with no carbon deposit.

Table 23 provides a summary of test procedure conditions for break-incharacteristics test, 5004DN, high speed durability tests 5004CN, highenergy durability tests 5030CN and the μ-v-p-t characteristic test 491N-494N for the materials shown in Examples 24-28 below.

                  TABLE 23    ______________________________________    Test Procedure Conditions (Not Immersed Modification)    (Size 3 Plates)    ______________________________________            Break-in     High Energy  High Energy    Test    Characteristics                         Durability Test                                      Durability Test    Procedure            5004DN       5004CN       5030CN    ______________________________________    Level   Level A      Level A & C  Level A & C    Cycles  200 cycles   50 cycles    ←    Speed   3700 rpm     ←       3600 rpm    Inertia 2.17         ←       ←            kgcmsec.sup.2    Pressure            137.8 KPa    ←       ←    Temperature            100-110° C.                         ←       ←    Oil flow            0.757 lpm    ←       ←    Kinetic 15974 Joule  ←       15122 Joule    energy    Level   --           Level B      Level B    Cycles  --           5000 cycles  5000 cycles    Speed   --           6200 rpm     4000 rpm    Inertia --           1.98         5.30                         kgcmsec.sup.2                                      kgcmsec.sup.2    Pressure            --           --           --    Stop Time            --           *0.8 sec.    **0.95 sec.    Temperature            --           110-110° C.                                      100-110° C.    Oil flow            --           0.787 lpm    ←    Kinetic --           40865 Joule  45558 Joule    energy    Power   --           2.27 W/mm.sup.2                                      2.13 W/mm.sup.2    density    ______________________________________              μ-v-p-t Characteristics    Test Procedures              49IN-494N    ______________________________________    Level     Level A         Level B    Cycles    50 cycles       25 cycles    Speed     800 rpm         1400 rpm    Inertia   3.55 kgcmsec.sup.2                              ←    Pressure  48.7 KPa        97.4 KPa    Temperature              49IN = 30° C., 492N =                              ←              80° C.   ←              493N = 100° C., 494N =                              ←              120° C.  ←    Oil flow  0.757 lpm       ←    Kinetic energy              1223 Joule      3745 Joule    Level     Level C         Level D    Cycles    25 cycles       25 cycles    Speed     2600 rpm        3600 rpm    Inertia   3.55 kgcmsec.sup.2                              3.55 kgcmsec.sup.2    Pressure  194.8 KPa       292.2 KPa    Stop Time --              --    Temperature              491N = 30° C., 492N =                              491N = 30° C., 492N =              80° C.   80° C.              493N = 100° C., 494N =                              493N = 100° C., 494N =              120° C.  = 120° C.    Oil flow  0.787 lpm       ←    Kinetic energy              12916 Joule     24761 Joule    Power density              --              --    ______________________________________     Note:     *In level B, adjust apply pressure to maintain 0.8 seconds stop time     within 175th cycles.     **In level B, press start at 140 KPa, adjust the pressure to maintain 0.9     seconds stop time by 175th cycles.

EXAMPLE 24

The following fibrous base materials, in percent, by weight, are used inthe examples below.

Example P is a two layer fibrous base material comprising a primarylayer of about 45% fibrillated aramid fibers (CSF about 450-500), about10% synthetic graphite, about 40% diatomaceous earth, and optionallyabout 5% optional filler, such as aramid pulp, and a secondary layer ofabout 3-5% carbon particles. In certain embodiments, it is desirable touse a retention aid to help adhere the carbon particles on the surfaceof the fibrous base material.

Example Q is a two layer fibrous base material comprising a primarylayer of about 45% fibrillated aramid fibers (CSF about 450-500), about23% synthetic graphite, about 27% diatomaceous earth, and optionallyabout 5% optionally filler such as aramid pulp, and a second layer ofabout 3-5% carbon particles.

Example R is a two layer fibrous base material comprising a primarylayer of about 25% less fibrillated aramid fibers (CSF about 450-500),about 45% carbon particles and about 30% cotton fibers, and a secondarylayer of about 20% carbon particles. In certain embodiments, it isdesirable to use a retention aid up to about 20% Alum to a pH4.5 to helpadhere the carbon particles on the surface of the fibrous base material.

Table 24 below shows results of a break-in test using a phenolic resin,for each of the fibrous base materials shown in Examples P, Q and R andthe percent resin pick-up for each fibrous base material is as shown.

Table 25 below shows the break-in characteristics for the fibrous basematerials for Examples P, Q and R saturated with a silicone resin B,wherein each fibrous base material has a percent resin pick-up as shown.

                  TABLE 24    ______________________________________    Break-In Test               39%          40%    41%    Pick-Up    Ex. P        Ex. Q  Ex. R    ______________________________________    μ(mid)    cycle 1    0.107        0.101  0.132    cycle 50   0.12         0.12   0.122    cycle 100  0.121        0.12   0.116    cycle 200  0.126        0.128  0.119    % change   17.76        26.73  -9.85    ______________________________________

                  TABLE 25    ______________________________________    Break-In Test            Raw Paper            Ex. P    Ex. Q        Ex. R            Pick-Up    Cure      61%        60%          65%    Condition silicone resin B                         silicone resin B                                      silicone resin B    ______________________________________    μ(mid)    cycle 1   0.156      0.146        0.144    cycle 50  0.162      0.154        0.137    cycle 100 0.157      0.157        0.145    cycle 200 0.162      0.153        0.142    % change  3.85       4.79         -1.39    Stop time    cycle 1   0.79       0.821        0.808    cycle 50  0.738      0.752        0.826    cycle 100 0.745      0.748        0.816    cycle 200 0.749      0.748        0.807    % change  -5.19      -8.89        -0.11    ______________________________________

It is noted that for the high carbon particles deposit fibrous basematerials (Example R) saturated with phenolic resin and non-phenolicresin, the dynamic coefficient of friction value and the stop time didnot change after the 200 cycles test.

For papers with the low percentage of carbon particle content on thefibrous base material (Examples P and Q), the silicone resins helpstabilize the dynamic coefficient of friction values within 20 cycles.In data not shown, it took 60 cycles for a phenolic/silicone resin tostabilize and about 80 cycles for a phenolic resin and 100 cycles forthe phenolic resin system to stabilize.

The stop time became constant after 20 cycles for the pure siliconeresins, while it took 80 cycles to reach the constant stop time for thesilicone blend (data not shown). The phenolic resin examples shown inTable 24 needed about 100 cycles to level of stop time.

In certain embodiments, the break-in behavior depends on the degree ofcarbon coverage on the surface of the fibrous base material and on thecompositions of the primary layer formulation (in various embodiments,sometimes the resin type is also to be considered in controlling thebreak-in behavior).

EXAMPLE 25

The following fibrous base materials, in percent by weight, are used inthe examples below. Each example comprises about 20% less fibrillatedaramid fibers (CSF about 580-640), about 20% synthetic graphite, about20% diatomaceous earth, about 35% cotton fibers, and optionally about 2%latex. A secondary layer for each of the following examples comprisedvarious percentage by weight of carbon particles.

Example S--0% carbon particles;

Example T--5% carbon particles;

Example U--10% carbon particles;

Example V--15% particles; and

Example W--20% carbon particles.

Table 26 provides break-in test data for Examples S, T, U, V and Wsaturated with a phenolic resin and cured at 350° F. for 30 minutes. Thecoefficient of friction for the mid, initial, final coefficients offriction are shown. Also, the stop time is shown. Table 27 also showsthe surface carbon coverage as percent of area and the saturated paperpore size and liquid permeability. The higher mean flow pore diameterindicates that the friction material is more likely to have lowerinterface temperature because of more efficient dissipation in theirtransmission due to better automatic transmission fluid flow ofmaterials out the porous structure of the friction material. Therefore,when a friction material initially starts with larger pores, more openpores remain during the useful life of the friction material.

                                      TABLE 26    __________________________________________________________________________    Break-In Test    (Procedure 5004D)    Coverage (% By            Ex. S  Ex. T  Ex. U  Ex. V  Ex. W    Weight) Resin            0%, phenolic                   5%, phenolic                          10%, phenolic                                 15%, phenolic                                        20%, phenolic    Cure Condition            350° F./30 min                   350° F./30 min                          350° F. 30 min                                 350° F./30 min                                        350° F./30 min    __________________________________________________________________________    μ(mid)    cycle 1 0.108  0.122  0.125  0.130  0.129    cycle 50            0.121  0.124  0.118  0.119  0.109    cycle 200            0.127  0.127  0.125  0.125  0.110    % change            17.6   4.1    0.0    -3.8   -14.7    μ(initial)    cycle 1 0.130  0.140  0.143  0.137  0.144    cycle 50            0.153  0.140  0.133  0.131  0.128    cycle 200            0.154  0.145  0.149  0.138  0.122    % change            18.5   3.6    4.2    0.7    -15.3    μ(final)    cycle 1 0.109  0.124  0.130  0.130  0.133    cycle 50            0.122  0.127  0.123  0.122  0.118    cycle 200            0.133  0.130  0.123  0.129  0.114    % change            22.0   4.8    -5.4   -0.8   -14.3    stop time    cycle 1 1.078  0.963  0.954  0.939  0.925    cycle 50            0.903  0.889  0.911  0.917  0.956    cycle 200            0.861  0.863  0.899  0.898  0.962    % change            -20.1  -10.4  -5.8   -4.4   4.0    Sat. paper pore            8.31   6.13   7.10   7.16   7.72    size(μm)    Liquid  0.127  0.111         0.085  0.080    permeability(cm.sup.2)    Surface carbon            2.0%   25.0%  35.0%  49.0%  90.0%    coverage(area%)    __________________________________________________________________________

Table 27 shows the shear strength for Examples T, U, V and W. The higherthe shear strength, the better the mechanical strength the frictionmaterial has, which means that more pressure is needed to shear thefriction lining.

The shear strength friction materials of the present invention aregreater than those for conventional materials. The use of the lessfibrillated fibers and the resulting porous structure of the frictionmaterial provides increased thermal resistance of the friction material.The fiber geometry not only increases thermal resistance, but alsoprovides delamination resistance and squeal resistance. In addition, thepresence of the synthetic graphite particles and at least one fillermaterial aids in increasing the thermal resistance, maintaining a steadycoefficient of friction and increasing the squeal resistance. Inaddition, the average pore size for the friction material of the presentinvention ranges from about 0.5 μm to about 120 μm in diameter and incertain embodiments about 6 μm to about 50 μm in a preferred embodiment.

Table 27 also shows the compression/relaxation studies. These testsreport the effect on paper caliber caused by repeatedly pressing on asample and releasing the sample through a series of different pressures.These readings provide an indication of the internal resistance to setor compacting during the processing. The examples show good elasticitywhich allows for more uniform heat dissipation during use of thefriction materials, since the fluid in the transmission or brake canrapidly move through the porous structure. Further, the increaseelasticity provides more uniform pressure or even pressure distributionon the friction material, such that uneven lining wear or separatorplate "hot spots" are eliminated or minimized.

                                      TABLE 27    __________________________________________________________________________    2 Ply Carbon Materials    Trial #          Ex. S Ex. T Ex. U Ex. V  Ex. W    __________________________________________________________________________    Shear psi          357   351   292   337    199    comp-set          0.067/0.013                0.068/0.014                      0.078/0.011                            0.067/0.014                                   0.061/0.014    300/1500psi          0.201/0.041                0.197/0.038                      0.212/0.040                            0.210/0.049                                   0.237/0.068    __________________________________________________________________________

Referring now to FIGS. 2-30, surface profiles for separator plates areshown. FIG. 25 shows a new separator plate having a surface roughness ofabout Ra 6.0 μin.

FIG. 26 shows Example S having 0% carbon material tested, having an Raof about 7.6 μin.

FIG. 27 shows Example T having about 5% carbon material tested, havingan Ra of about 6.0 μin.

FIG. 28 shows Example U having about 10% carbon material, having an Raof about 5.6 μin.

FIG. 29 shows Example V having about 15% carbon material, having an Raof about 11.5 μin. with a scar depicted thereon.

FIG. 30 shows Example W having about 20% carbon material, having an Raof about 11.7 μin., having two scars shown thereon.

Table 28 shows the percent of area carbon for Examples S, T, U, V and Wbefore the tests and after the tests.

                  TABLE 28    ______________________________________    Area % of    Carbon    Ex. S  Ex. T     Ex. U Ex. V   Ex. W    ______________________________________    Before Test              5%     35%       52%   61%     73%    After Test              3%     52%       65%   67%     80%    ______________________________________

The above data in Tables 26 and 27 and in FIGS. 25-30 show a series offibrous base materials with different percentage of carbon coverage onthe surface which were tested for break-in behavior. It is to be notedthat Examples T and U having a 5% and 10% carbon coverage, by weight,have a better break-in behavior than Example S having 0% carboncoverage. Both Examples T and U have similar mid point dynamiccoefficient of frictions as Example S at cycle 200.

The Example W, having about 20% carbon coverage, had a large drop off ofthe dynamic coefficient and also a lower dynamic coefficient of frictionthan Example S having 0% carbon coverage at cycle 200.

It is to be noted that there is a relationship between the percentage ofdynamic coefficient of friction change and the surface carbon coverage(area of percent). There is also a relationship between the percent stoptime change and the surface carbon coverage (area of percent). Theserelationships are shown in FIGS. 31 and 32.

EXAMPLE 26

Example 26 shows the effect of carbon coverage on fibrous base materialsin long-term durability tests. Example X comprises about 25% aramidfibers (CSF about 450-500), about 30% cotton fibers, about 20% syntheticgraphite and about 25% diatomaceous earth.

Example Y comprises about 25% aramid fibers (CSF about 580-640), 20-30%cotton fibers, about 20-25% synthetic graphite and about 20-25%diatomaceous earth. Example T is as stated above and Example Z,comprises about 40-50% aramid fibers (CSF about 450-500), about 20-25%synthetic graphite, about 25-30% diatomaceous earth, and optionallyabout 0-7% aramid pulp.

The Example T resin has very good break-in behavior and the very goodhigh speed durability. It should be noted that Example Y also had abetter durability than the Example X even though neither Example Y nor Xhad carbon particles.

FIG. 33 shows the initial coefficient of friction change for Examples X,T and Y. FIG. 34 shows the initial stop time change for Examples X, Tand Y.

EXAMPLE 27

The high energy durability test according to Procedure 5030CN are shownin FIG. 35.

FIG. 35 shows the stop time fade for Examples T, Z and AA. It is notedthat the Example T had a stop time fade at almost 4000 cycles, while theExample AA had a stop time fade of greater than 2500 cycles and that thestop time was less than about 1.05 seconds. It is seen in Example T thatit has the best durability of all materials tested under this 5030CNprocedure showing high inertia durability. Example T is the carbondeposit material (5% carbon deposition). Example AA and Z are non-carbondeposit materials (0% carbon deposit).

EXAMPLE 28

As seen in Table 29 below, the Example T which has about 5% carbonparticle secondary layer shows good friction behavior, including goodcurve shape ratings and good coefficients of frictions as compared withExamples X and Y.

FIGS. 36, 37 and 38 show the coefficient of friction curved shapes forExample X which does not contain carbon deposit for levels A, B, C and Dshowing the initial mid point and final coefficient of frictions.

FIGS. 36-37 show the engagement torque characteristics for frictionmaterials without a carbon deposit (relative rotation speed=1400 RPM inFIG. 36 and relative rotation speed=2400 RPM in FIG. 37). FIG. 38 showsthe dynamic coefficients of friction (μ) for the friction materialswithout a carbon deposit at various rotation speeds.

FIGS. 39, 40 and 41 show the curve shapes for the Example T comprising afibrous base material having a less fibrillated aramid fibers (CSF about580-640) and a secondary layer of about 5%. The Example T is impregnatedwith a phenolic resin at about 35% to 40% pick-up. FIGS. 39, 40 and 41show the initial mid point and coefficient of friction for levels A, B,C and D.

FIGS. 39 and 40 show the engagement torque characteristics for frictionmaterials with a 5% carbon deposit (relative rotation speed=1400 RPM inFIG. 39 and relative rotation speed=2400 RPM in FIG. 40). FIG. 41 showsthe dynamic coefficients of friction for the friction materials with a5% carbon deposit at various rotation speeds.

The FIGS. 36-41 show that the Example T has good curve shape rating andgood coefficients of friction. The fibrous base material having asecondary layer of carbon deposit has a higher friction durability dueto higher thermal conductivity, larger pore size and greater liquidpermeability of the primary layer.

                  TABLE 29    ______________________________________    Torque Curve Shape Evaluation               Ex. T    Ex. X     Ex. Y    ______________________________________                 5%-carbon    Rate B       4/5        1         1    C            4          1         1    Coeff. A     0.143      0.132     0.134    B            0.137      0.127     0.132    C            0.129      0.121     0.120    D            0.131      0.125     0.119    Break-in %   *2.0       *2.1%     *2.1    Stop-time/μ                 0.7        6.40      1.5    ______________________________________

EXAMPLE 29

Table 30 below provides a summary of test procedure conditions for thehigh speed durability test 5004CN for a loose carbon friction material,Example BB, and a carbon deposit friction material, Example CC. TheExample BB is a friction material comprising a primary layer having abasis weight of 172 lbs. and comprising less fibrillated aramid fibers,synthetic graphite, filler, 2% latex retention aid, and optionallycotton fibers and having a secondary layer of about 5 lbs. carbonparticles (approximately 5%, by wt., based on the weight of the fibrousbase material) with no retention aid as compared to the Example CCfriction material comprising the same primary layer and having asecondary layer comprising about 5 lbs. carbon particles (approximately5%, by wt., based on the weight of the fibrous base material) and 5%latex material. Assembly or core plates were lined with theabove-described friction materials impregnated with a phenolic resin atabout 35% resin pickup to form a pack for testing. The loose carbonfriction material (Example BB) failed at 1050 cycles, while the carbondeposit on material Example CC passed 3100 cycles. The coefficient offriction for levels A, B and C indicate that the carbon deposit fibrousbase materials perform consistently and the stop times are consistentlyacceptable.

                  TABLE 30    ______________________________________    5004CN Test Procedure    (Medium-high speed durability test)    ______________________________________    Basis weight    172          172    Carbon concentrate                    5 lb         5 lb    Top layer retention aid                    0            5%    primary layer latex                    2%           2%    Resin Pickup %  35%          35%    Total wear (in)              0.0089    Friction plate               glazing    condition                    abrasion    Steel plate                  heat stains    condition                    grayish strains    Stop Time (Sec.)    A               0.893        0.866    B               0.84         0.877    C                            0.957    Level A (at 50 cycles)    Static μ     0.088        0.099    Initial μ    0.15         0.154    Midpoint μ   0.134        0.133    Final μ      0.133        0.134    Level B (at 3050 cycles)                    fail @ 1050 cycle                                 pass 3100 cycles    Static μ     0.095        0.076    Initial μ    0.109        0.106    Midpoint μ   0.112        0.104    Final μ      0.108        0.1    Level C (at 3100 cycles)                    N/A    Static μ                  0.1    Initial μ                 0.14    Midpoint μ                0.122    Final μ                   0.125    ______________________________________

EXAMPLE 30

The percent of carbon particle loss was compared to the percent ofretention aid present in the secondary layer. FIG. 43 provides theresults of a peel test for friction materials with and without aretention aid. It is seen that the carbon deposit friction materialswith a latex retention aid only lost between 2 to 3% carbon particles,while the friction materials without the retention aid lost betweenabout 6-18% carbon particles.

INDUSTRIAL APPLICABILITY

The present invention is useful as a high energy friction material foruse with clutch plates, transmission bands, brake shoes, synchronizerrings, friction disks or system plates.

The above descriptions of the preferred and alternative embodiments ofthe present invention are intended to be illustrative and are notintended to be limiting upon the scope and content of the followingclaims.

We claim:
 1. A non-asbestos friction material comprising a fibrous basematerial impregnated with at least one curable resin, the fibrous basematerial comprising a primary layer of a plurality of less fibrillatedaramid fibers having a freeness of at least about 450 on the CanadianStandard Freeness (CSF) index; synthetic graphite, and, at least onefiller material; and a secondary layer comprising carbon particles andat least one retention aid on at least one surface of the primary layer.2. The friction material of claim 1, wherein the retention aid comprisesa latex material.
 3. The friction material of claim 1, wherein theretention aid comprises a resinous material.
 4. The friction material ofclaim 1, wherein the retention aid comprises a sizing agent.
 5. Thefriction material of claim 1, wherein the retention aid is present inamounts ranging from about 2 to about 28%, by weight, of the carbonparticles.
 6. The friction material of claim 1, wherein the secondarylayer of the carbon particles is present in a thickness of about 10 toabout 50 microns to provide high heat resistance and substantiallyuniform coefficient of friction to the friction material.
 7. Thefriction material of claim 1, wherein the secondary layer comprisesabout 0.2% to about 30%, by weight, of carbon particles, based on theweight of the fibrous base material.
 8. The friction material of claim1, wherein the secondary layer comprises about 5% to about 15%, byweight, of carbon particles, based on the weight of the fibrous basematerial.
 9. The friction material of claim 1, wherein the secondarylayer comprises about 3 to about 5%, by weight, of carbon particles,based on the weight of the fibrous base material.
 10. The frictionmaterial of claim 1, wherein the carbon particles cover about 3 to about90% of the surface area of the primary layer.
 11. The friction materialof claim 1, wherein the carbon particle size ranges from about 6 toabout 50 microns.
 12. The friction material of claim 1, wherein the lessfibrillated aramid fibers have a freeness about 300-700 on the CanadianStandard Freeness index.
 13. The friction material of claim 1, whereinthe less fibrillated aramid fibers have average fiber lengths in therange of about 3 to 6 mm.
 14. The friction material of claim 1, whereinthe synthetic graphite is made by graphitization at temperatures ofabout 2800°-3,000° C. and has a size ranging from about 20 to about 50microns in diameter.
 15. The friction material of claim 1, wherein thefiller comprises diatomaceous earth.
 16. The friction material of claim1, wherein the fibrous base material defines pores ranging in meanaverage size from about 2.5 to about 12 microns in diameter.
 17. Thefriction member of claim 1, wherein the friction material has readilyavailable air voids of at least about 50%.
 18. The friction material ofclaim 1 comprising about 10 to about 50%, by weight, less fibrillatedaramid fiber; about 10 to about 35%, by weight, synthetic graphite;about 20 to about 45%, by weight, filler material; and about 0.2% toabout 20%, by weight, carbon particles.
 19. The friction material ofclaim 1 comprising in percent, by weight, about 20 to about 30%, byweight, less fibrillated aramid fibers; about 15 to about 35%, byweight, synthetic graphite, about 20 to about 30%, by weight, filler;about 0 to about 40%, by weight, cotton fibers; and about 2% to about20%, by weight, carbon particles.
 20. The friction material of claim 12,wherein the fibrous base material comprises about 20% to about 40%cotton fibers.
 21. The friction material of claim 1, wherein the primarylayer includes about 1 to about 5% latex binder, by weight, based on theweight of the primary layer.
 22. The friction material of claim 14,wherein the friction material comprises approximately 25 to about 60%resin, by weight.
 23. The friction material of claim 1 impregnated witha phenolic resin or a modified phenolic resin.
 24. The friction materialof claim 1 impregnated with a mixture of a phenolic resin and a siliconeresin wherein the amount of silicone resin in the mixture ranges fromapproximately 5 to approximately 80%, by weight, based on the weight ofthe mixture, the friction material exhibiting high heat resistance andsubstantially uniform coefficient of friction.
 25. The friction materialof claim 24, wherein the phenolic resin is present in a solvent materialand the silicone resin is present in a solvent material which iscompatible with the solvent material of the phenolic resin.
 26. Thefriction material of claim 24, wherein the amount of silicone resinpresent in the silicone-phenolic resin mixture ranges from about 20 toabout 25%, by weight, based on the weight of the mixture.
 27. Thefriction material of claim 24, wherein the amount of silicone resinpresent in the silicone phenolic resin mixture ranges from about 15 toabout 25%, by weight, based on the weight of the mixture.
 28. Thefriction material of claim 23, wherein the modified phenolic resincomprises an epoxy phenolic resin.
 29. The friction material of claim28, wherein the amount of epoxy resin present in the epoxy phenolicresin ranges from about 5 to about 25%, by weight, based on the weightof the epoxy phenolic resin.
 30. The friction material of claim 28,wherein the amount of epoxy resin present in the epoxy phenolic resinranges from about 10 to about 15%, by weight, based on the weight of theepoxy phenolic resin.
 31. A process for producing a non-asbestosfriction material comprising mixing less fibrillated aramid fibershaving a freeness of at least about 450 on the Canadian StandardFreeness (CSF) index with synthetic graphite and at least one filler toform a fibrous base material, coating at least one surface of thefibrous base material with a mixture of carbon particles and at leastone retention aid, impregnating the carbon particle coated fibrous basematerial with at least one phenolic resin or modified phenolic resin,and thereafter curing the impregnated fibrous base material at apredetermined temperature for a predetermined period of time.
 32. Aprocess for producing a non-asbestos friction material comprising mixinga phenolic resin with a silicone resin, impregnating the fibrous basematerial of claim 1 with the silicone-phenolic resin mixture, andthereafter heating the impregnated fibrous base material to cure thephenolic resin and the silicone resin.